There are quite a few companies providing VoIP services on the Apple iPhone. VoIP optimizes the transmission of voice over Internet. Here’s a quick overview of some of the notable ones.

Fring, an Israeli company, brings its Voice Over Internet Protocol application to the iPhone. The application enables users to talk, interact and chat with other fringsters, and online communities which is powered by the iPhone Wi-Fi. The prerelease version allows users to add contacts from their online communities. Users can either make free or nominal cost mobile calls over Wi-Fi. Users can also chat with their online contacts, whether their friends are using their Internet devices or mobile phones. A single integrated contact list combines contacts from all their online communities.

Another VoIP provider is Truphone. Truphone enables the integration of iPhone and VoIP with Facebook. “People today use multiple tools to communicate in different ways at different times, but this multiplication of options can serve to confuse consumers,” Tagg, spokesperson of Truphone, says. “By providing the Facebook community with free calls to real phones, Truphone will genuinely help bridge the worlds of traditional and Internet telephony.”

Mo Call is another VoIP service available for the iPhone. It is similar to Jajah, in that it enables access to call back service which is low cost. It is simple enough to use. All you have to do is point your Safari to mo-call.mobi.