If you subscribe a VoIP to PSTN (=classic telephony) account to a telecom provider, you can reach everyone that has a "classic" phone line.
FCC Phone available on FCC Member only.
List of supported features:
-Audio with the following codecs: Speex8
-Vdeo with the following codecs: H264
-Address book integration
-DTMF (telephone tones) support using SIP INFO or RFC2833