Does I pay only from GPRS or is there somekind of charge per message I send??
Agile Messenger
Only GPRS (send AND receive). Doesn't use many KBs either, only about half a KB a message (depending on the length of the message obviously]. And when you're in standby (connected but no sending/receiving) it hardly uses any data. I am connected to Agile almost 24/7, and use it as a cheap and fast alternative to SMS.
Yes I use it also and it works very well with minimal traffic which = minimal traffic costs.