still not possible........

ok not possible

there are restrictions? is needed a license for example to offer a voip service in Serbia?
some license as telecomunication provider, internet provider etc..

I've friends that could help to set up / start up voip in Belgrade, if somebody can help
and tell which could be the difficulties or requirements to do that I can speak with them and hear
what they think

K.

Problem is that isn't legal to use fixed phone lines in combination with VOIP, not exist licence can permit that. This means to users can't call your company from home through fixed phone line, than users must walk to VOIP service company and make calls from there. In that case, not needed any licence.

Are you sure???
Why i don't see anywhere in serbia public VOIP pay phones, like in Bulgaria or other places?
You can place payphones anywhere without using fixed telephone lines (wireless comes to mind).

Only wireless service with good coverage here is GPRS. Up until recently, the incumbent telecom (landline) provider had full control even over other (allegedly competition) GSM provider.

Recently Telenor stepped in and both this other GSM network but we are still waiting to see what will they offer. However, wouldn't they hurt their own income if they enable VoIP service to a third party company?

Besides, this incumbent telco also owns all the international trunks so we are basically in their grip when it comes to VoIP, as all ISP's use their lines. It is quite a political (or even worse: corruptionist, extortionist, monopolist) problem, not a technical one.