Use Yahoo or Skype on your Mobile
– www.fring.com. VoIP client and nothing to do with the embedded Nokia Internet Telephony client. Works best over WLAN and 3G as 2G networks have often longer packet delays that impact voice quality.
– www.iSkoot.com. Uses your local and normal GSM minutes to make normal GSM calls – not totally “free” VoIP, but if can use your local GSM minutes to call your Skype buddy in another country, that’s pretty good deal. Works everywhere as long you have just GSM network available and GPRS packet connection for Skype presence information.