Hello Alessandro.
First of all please write just 1 post, there's no need to write 4 and remember English is the only language used on this forum.
As I wrote back by e-mail in Italian, ERONET is the Bosnian-Croatian operator so it should have good coverage in Međugorje since it's in the Hercegovina region where mostly Croatian Catholics live.
Their prepaid offer is called
!hej and as far as I know you can buy the prepaid card without any document (in any case you'll have your id).
Here are the rates (click on CJENIK !HEJ TARIFA):
http://www.hteronet.ba/privatni-kori.../hej-savrsena/
International calls are "Međunarodni pozivi". Italy should be in Zona I.
You can find more information in English about data bundles here:
http://prepaidwithdata.wikia.com/wik...nd_Herzegovina
About the rates for calling a Bosnian number from Italy it really depends on your Italian operator. I think the best solution would be to use Skype or something similar.
As I wrote in my e-mail, I think a cheaper solution would be to buy an IZI prepaid card, which is a virtual operator roaming on BH Telecom network which has much cheaper rates (half to call Italy). Here in Slovenia you can buy IZI cards at petrol stations, it's probably the same in Bosnia.