Yup. I made the switch a few months back. Sipdroid has been something of a headache (I suspect it's more PBXes.org) but every time I'm having a problem with it I just repeat to myself "$70 a month."
ha! WORD. people have been telling me for YEARS "hey man you need a better phone. get better carrier!" then i tell them i pay $30 a month. then you can see in their eyes all the months adding up of paying at least $50 more then i have. thousands of dollars flash before their eyes