VoIP takes advantage lots of hybrids and variations, and now wireless mobile virtual network operator (MVNO) Tokiva has added instant messaging on mobiles to the mix as a way to initiate a packetized voice call.

The Toronto-based operator said Monday that its IM-To-Call service is available immediately on leading IM clients, including MSN Messenger,Yahoo (NSDQ: YHOO) Messenger, AOL Messenger, and Google (NSDQ: GOOG) Talk. Its general availability follows a beta test that began in January, Tokiva said in a statement.

Users don't need to download any software to make wireless VoIP calls. Registered users receive an invitation to add Tokiva as a buddy on their IM lists, and then send an instant message to Tokiva to call. Tokiva calls back, either to the user's landline or mobile phone, then immediately connects the caller to the desired number.

"Using Tokiva can save up to 90% of normal call costs," the MVNO claimed, "because the calls are carried by Tokiva's global VoIP network that has a footprint in over 185 countries."

Tokiva said its customers also tend to be heavy users of IM, so that the Tokiva IM-To-Call service is a natural extension to what they are already doing. "Tokiva is connecting text-based IM systems with voice-based phone networks in a simple yet powerful way," said Tong Li, founder and chief executive of Tokiva.

According to figures from ComScore Media, there are 90 million instant messaging users in the United States. By the second quarter of 2008, Tokiva said it plans to support QQ Messenger, the most popular IM systems in China, which counts 520 million users.