You may want to consider RTCOMM and SIP. It's a little harder to find a good provider, but the prices are swell (sometimes lower than skype, depending on the provider), and you needn't worry about compatibility as its standardised (protocol + codecs).

For example, in Toronto vBuzzer offers unlimited local plans for $50CDN/year (~$40US).

You can also buy a device to hook up your phone to your home router and 'share' your number; have your phone ring at home and on your NIT.

Plus if you're a bit of a hacker, there's little end to what you can do with an installation of Asterisk PBX on your home server.

YARR!
}:^)~
Capt'n Corrupt