Try tringme.com- TringMe - Web based Telephony
Sometimes it works great. Sometimes...
But at least is free via WIFI, it doesn�t work via 3G
If you get another one just tell me
Bests
TATA
If you are one a GSM carrier, there are a couple of true VOIP apps out there. I'm not sure which services they will connect with, though.
If you are on a CDMA carrier, the chipset in the current models cannot do VOIP. There is a Skype app (Verizon only), and a few other VOIP apps (like Vonage). All of them make phone calls into the service, then routes the call over VOIP, but they aren't true VOIP.
I don't know where you are located or where you want to call but UMA makes calls for free over wifi and has been standard on all T-Mobile BlackBerry phones for years now. Google Voice works perfectly for cheap long distance calls.
Try Jajah. I found it from the Blackberry App World and its great. In most cases, its free between Jajah users. If between other users, they charge very small fees.
Posted from my CrackBerry at wapforums.crackberry.com
VoIP calling stand for voice over Internet Protocol. VoIP provides a calling facility on internet. It is widely used in many organizations or companies to make national as well as international calls in very cheap prices.