Does your girl friend have broadband in the US? Do you have a landline in the UK? Do you have broadband.
Calling the UK is really cheap from the US with a calling card. I use onesuite.com, it is two something cents a minute. In the other direction, look at call1899.com. Half a p a minute. They also, have a VOIP program. I Does your girl friend have a triband? One of the better prepaid offerings comes from 711.com. Their speakout wireless phones are effectively free and the per minute rate is $US0.20 a minute. It works nationwide in the US, and has a one year expiry. Remember that in the US incoming calls come out of your bucket of minutes.