Free VoIP apps for WiFi iPad 2

[2high2aim]

I was looking into VoIP and trying to find a free VoIP app for my WiFi iPad2. Please list free and low costing app (only if they are worth it)
Thus far I found

Free App:
Line2
Whistle Phone

Low Cost App:
TAT ($2/mo) (not free but relatively cheap

 

[bperrella]

Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_2_8 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8E401 Safari/6533.18.5)

Talkatone combined with google voice account. 100% free and unlimited

 

[PracticalMac]

Skype
Yahoo Messenger.

HeyTell is not a real-time VoIP, but sends voice mail.