The arrangement means that users can make voice calls to contacts using most of the popular IM and VoIP services, including Gizmo5 and Skype, in over 50 countries.
The Nimbuzz service, which runs on all Internet-capable mobile phones, detects when the handset is out of Wi-Fi or 3G range and steps in.
It requests permission to automatically dial a local access number and route the call over the Internet.
With most mobile plans, such calls are free except for a low charge (if any) to the local access number.
The Nimbuzz software client determines the correct access number to dial from the user’s Nimbuzz profile.
Headquartered in Brussels, Belgium, Voxbone provides worldwide local and toll-free phone numbers over its own private intercontinental VoIP network.
Tobias Kemper, Nimbuzz head of communications, said the intention is to make Nimbuzz a truly mass-market application.
"Not one limited to this mobile platform, or that chat/calling network, or a particular click sequence," he said.
"By adding the DID numbers supplied by Voxbone, we can provide reliable mobile VoIP outside of Internet range and over 2G networks in over 50 countries, with any Internet-enabled handset and no change in user behavior."
Currently growing at a rate of over 750,000 sign-ups per month and operating in 200 countries, Nimbuzz offers mobile VoIP, chat, location, file sharing and MMS services under one application.
It works across popular communities and social networks, including Skype, Windows Live Messenger, Yahoo! Messenger, ICQ, GoogleTalk, AIM, Facebook and MySpace.
Nimbuzz VoIP also reaches PSTN phones through Skype-Out, using any of 10 VoIP third-party VoIP services (including Skype).
A full phone keypad is part of its interface, along with the multi-service buddy list.