Hoiio is an service that lowers your phone bill, especially if you are always exceeding your bundled talktime, or if you are always making international call or SMS.
Hoiio is a must have app for a windows mobile phone! Whats more, it is free to register, prepaid based (no monthly subscription) and it is giving $1 bonus credits upon registering!
http://content.hoiio.com/localmobilecall.html
videos:
http://www.youtube.com/watch?v=G_tCZjIOhN8
http://www.youtube.com/watch?v=jwFJMaxkG_8
just tried it on samsung omnia and it works!