For e-mail, there is an interesting option for slow, expensive, high latency circuits. Check out
www.uuplus.com It's a bit extreme for most of us but if you were hooking up over Iridium, I'd recommend it. Some mail programs allow you to download the first N lines. You may also be able to use a mail server that strips out unnecessary headers. Also, your server sould implement agressive SPAM filtering. Having a unique address just for your mobile and using a whitelist would keep much of the junk mail at bay. For web surfing, always use the WAP or Mobile interface to a site if they have one.