Do I understand you right that you want to have several computers like a cyber cafe and let people make International calls from or do you just want to provide the IP phone service without the computers?
You can add VoIP to a computer with 56K for a $15.00 headset or a $49.95 USB phone.
If you don’t want to use computers then you could use one wireless router $50.00/$100.00 and WI-FI $250.00 phones on 100K bandwith connection per phone in use at a time. no monthly VoIP service for PC to PC calls and prepay PC to PSTN calls.
If you have more questions contact me at email@example.com