Another VoIP app has been approved by Apple for use on iPhone and iPod Touch - and it's not Google Voice.

All-you-can-talk voice service Vonage announced today that its app has been given the go-ahead for use on the iPhone.

Vonage charges a monthly subscription (from £6 in the UK or $25 in the US) for unlimited free calls to landlines, and some international numbers and mobiles.

A world of free calls

Vonage joins other VoIP services available in the App Store, such as Skype, iCall, FriendCaller and Nimbuzz - all of which use the gadget's Wi-Fi links to initiate calls. Apple has said that its agreement with AT&T in the US prohibits it from allowing a customer to use AT&T's mobile network to originate or terminate a VoIP session, without first getting AT&T's permission.

The US Federal Communications Commission launched an investigation after it thought that Apple had rejected Google Voice application. The FCC wanted to know whether AT&T had influenced the decision. However, Apple says that it still reviewing the Google Voice application, which apparently infringes other agreements with AT&T by uploading a user's entire phone book to Google's servers.

Whether or not Google Voice makes it to the App Store in its current form, two things are certain: Apple is happy to host VoIP services despite any grumblings from its exclusive mobile network partners; and Google is powerful enough to force an FCC investigation even before any wrong-doing has been demonstrated.

Vonage has said that it is currently conducting a beta test of its app and that general availability will be announced "at a later date".