I just made the switch myself. The only thing is; it cost me the iPhone. Only Android phones have the WiFi calling on them. As a result, I had to give up my iPhone and switch to an S4. I have to say though it has been useful as I made crystal clear calls in the middle of nowhere (through hotel wifi) where att nor tmobile get good reception.

In the process with the cost of the new device included in the monthly payments I ended up saving about $80/month for a family plan of 3 phones.

I wish iPhone supported the WiFi calling! Maybe a google voice solution is under way.

If you travel internationally the fact that you can use your data connection (albeit on 2g) internationally without any roaming fees is superb. I would say make sure to get the right phone based on your needs but switch soon!