Questions, questions...
 

In spite of the efforts of many to help understand the world of "prepaidgsm" and other providers, there are many of us who are still faced with a lot of questions.
After several days surfing the net, I discovered how insufficient the information are.
1- SIM cards: there are different types but nobody tells you which one goes into your phone and, if you are like me, you don't know what you device can take.
2- I have still not understood the time management of those cards, buying more time has several options and if I grasp the literature, if you call to buy there is a charge but if you go to a retailer it is free???
3- If all the time is not used while abroad, is the credit still available on a future trip?
There are still other questions that are not very clearly answered or not at all.
Every site is making great efforts to help consumers but the whole thing is getting pretty confusing for non experts like me.
Simplicity would be welcomed and surely as profitable.

I am sort of a newbie too so I understand your confusion. It will help to know which countries you are traveling to and what you need the sim card for then perhaps someone on here can help sort out some of your questions.

As far as I know there are only two usual types of SIMs. A regular and a micro SIM. Micro SIMs are not used very much on many devices. They're used on iPad and the new iPhone 4.

I'm not sure what you mean by "time management." All prepaid accounts have some requirement to keep the account active. You either have to add more minute vouchers by a certain date or you have to place a billable call by a certain date in order to keep the account active.

An account's validity is determined by the carrier's terms. Most have six months or a year's expiry on the accounts by which time you must add more minute vouchers in order to retain any balance in the account. Other carriers don't necessarily require any more vouchers but require that you place a billable call every six months (T-Mobile is one such carrier and is what's required in the UK and in the NL and perhaps other T-Mobile countries as well.

Any credit you have in your account will continue as long as you follow the carrier's procedure i.e. to add vouchers or make billable calls depending on what the carrier requires.

Sorry it's all a bit confusing. The first confusion you seem to have (about the size of the SIM), is a relatively recent development by Apple. As mentioned above, up until the iPad and iPhone4, every GSM device in the world had exactly the same SIM card (with few exceptions). As it is you also have to remember that you will not be able to just use another operators SIM in your existing phone unless your phone has been 'unlocked' in order to be able to do so. Also you will have to check that your phone's built in operating frequencies exist in the country you are visiting. If in doubt, just post a specific question here which states the Phone's model, current operator and the country you intend to visit.

In terms of the rest of your questions, they really are very specific to operators. There are thousands of operators in the world, and tens of thousands of prepaid tariffs. We couldn't possibly generalise about them all. This forum has been set up so that people from around the world can interact with each other and discuss developments etc. In most cases, somebody who is knowledgeable about a tariff (usually in their own country) can recommend a SIM for a newbie like yourself who might not have any idea what to get due to information overload. That is why the specific question on where you are going, and what useage you will be requiring was asked.
I have a question as well. I have often heard people from North America referring to credit as "time" and "minutes". Is this still the case these days? Isn't this dead confusing in it's own right? How can a system of credit that is based on time compensate for changes in tariff when you go to different countries? When I first went to the USA in 1996, I ended up working in some little Hicksville and initially had to rely on a few prepaid phone cards (not SIM's) in order to keep in touch with family back in Europe. However the problem I consistently found was that these cards were always advertised on their "minutes", which signified how many long distance (national) minutes I could speak for with my credit. In most cases, I could not ever find out how many international minutes I would get on my card, until I actually tried to make a call with them. On one "100 minute card" that our employer generously gave all of his international staff as a welcome gift, I was pretty surprised that it gave us under 5 minutes of talktime to most European landlines! Some of the other staff mentioned this to our boss later on, but he could just not understand why a "100 minute" card was just not what it said on the pack? I totally understand the confusion. He had paid just under $10 for each card, which placed the price per minute at over $2/minute. Later on, we managed to find cards that gave us close to 100 minutes to Europe for our 10 bucks! (10c/min). I guess he was frustrated that he didn't get us those in the first place! ;)

Anyhow, in the rest of the world, prepaid credit is generally referred to by its monetary value. (In Dollars, Euros, Pounds etc.). The tariffs that you will see here on prepaidgsm and any links that you will follow through will generally state various destinations as a cost per minute. (e.g. 3cents/minute to call from A to B, 15c/min to call from B to A).

This has to do with the expiration of the SIM. Generally, most prepaid SIM cards expire after a certain period of inactivity, or a certain time after the last addition of credit to the account. Sometimes this can be very generous (most British SIMs require just one billable action from anywhere at least every six months or one year to stay active), so as long as you are able to meet the provider's guidelines, the SIM will indeed be available for use on a later trip. Often the expiration date for being able to receive calls on the account will be longer than that for being able to place calls.

Note that pretty much everywhere outside North America, you do not pay to receive calls ever, unless you are roaming in another country.

Just to add something more from the other people.
All the "time" information is always written (when known) in the single operators' pages here on PrepaidGSM.net under the word "Validty". In the same cell are usually listed the different recharge vouchers too and their validity, credit, bonuses, etc...
There's not 1 single rule, there are hundreds of different rules depending on the Country, the operator, the tariff...
You just need the patience to read carefully the National Operators pages. Then if you still have doubts you can ask here.

Also note that just about everywhere else outside North America differentiates between mobile and land lines, when it comes to how much callers are charged. So, callers calling your mobile will pay a premium. For example, it's cost about 1 US cent (free on a lot of carriers) to call a UK landline. However, calls to a UK mobile is easily 18 US cents and above. So, whatever card you end up getting, your callers should be made aware of this.

Something else:
To 1: Except of the new Apple stuff mentioned almost all GSM-phones are using the same kind of Sim-cards. So these Sims fit in all phones. So there is almost never a problem. But you have to check which bands are needed in the country / in the countries you want to visit. Most networks are using the 900 MHz band and the 1800 MHz band (Europe, Australia, Asia, Africa) but in the Americas you will find (almost only) 850 MHz and 1900 MHz band networks. And there are a few UMTS-networks like "3" (UK, At, Dk, Se, Au..) and "Melita" (Mt) which do not use GSM but UMTS. The best thing is to have a quad-band phone (850 MHz, 900 MHz, 1800 MHz and 1900 MHz band) which will work almost everywhere.
To 2: As mentioned, usually you top up your account with a value of money. "Time" does not matter, because in most countries you do not pay for incoming calls while being on your home network. Because calls to mobiles are more expensive then to landlines, in most countries the terminating fee is higher on mobiles ("Calling party pays").
To 3: Not every provider is allowing roaming for prepaid customers, or only limited (T-Mobile US prepaid does not roam in an other T-Mobile country!). To keep your number alive, you should have the possibility to use the Sim!

SIM lifetime
 

I must admit, even though I am an experienced traveler, I too am confused about how these PAYG plans work. For example, I have a SIM from Vodafone Romania purchased 7/14/10. I have a permanent local address and the ability to top up locally or abroad. I have registered the SIM with the website, which tells me that I have 9,78 euro credit, valid until 11/11/10. It offers me the ability to top-up (4 euro valid 30 days, 10 euro valid 60 days, etc etc). I have roaming enabled, can use the SIM abroad, and APN settings let me use data as well.

Help me process this info clearly and please correct my misunderstandings...

1. If I do nothing, after 11/11/10 my SIM will not be capable of making outgoing calls, but will receive calls? If so, until when?
2. If I do nothing, after 11/11/10 my credit is lost? If so, now to recover?
3. If I top up prior to 11/11/10, the SIM is extended for just the newly purchased lifetime, or does the SIM itself get extended 10 months but the ability to initiate calls extends only 30 days, 60 days, etc? this relates to the National Operators web page which uses notation like "4+10 months", which I don't understand.
4. Is topping up considered an activity which gives life to the SIM, or must there be a billable event like a phone call or text message?

ultimately, what must I do prior to 11/11/10 in order for me to keep the same number until I return in the summer of 2011?

Thanks!

Someone will correct me if I'm wrong, but with prepaid any balance of money in your account will remain as long as you refill with additional funds or for some carriers you need to make something billable (such as a call or a SMS) to extend the account further. As to your question number 4 I'm not sure whether topping up is considered an action, but my guess is that it does. I'd contact the carrier to be sure, but I'd think that the action of topping up would be sufficient.