A GrooVe Kind-of IP

I would give most of the credit to drastic improvements in Samsung hardware, Android OS, and Google's generosity, but GrooVe IP is the best VoIP App I've used.

The programmers over at snrb Labs have managed to develop a fairly solid application.  Users who are only interested in basic calling functionality can forego the paid App and get free calling over WiFi only.  I, however, have gone for the full app and can now make calls over 3G / 4G.

After using the to make at least 10 calls of varying lengths, I have come to the following conclusions.

1) If the signal for WiFi is poor, the call may drop, be static-y, or not start at all.
2) With a strong signal, there is no noticeable difference in the quality of audio, from non-VoIP calling.
3) Calls can be made from just about any Android OS from Eclair (2.0) to Jelly Bean (4.2).

Check it out on the Google Play store
(Sorry iPhone users)