I was forced to switch. I had an old $19.99 unlimited plan called smartphone dataconnect unlimited. When I got my Focus a couple years ago, they had to fight with the system to keep it, but they got it and I had no issues. This time around, I went to the MS store and the sales guy was having problems getting the system to take my plan. An AT&T rep happened to be there and said I could try buying the phone outright and seeing if my sim would at least give me 3G. I walked away and went to the AT&T store to see if I got a different response. Same thing. I asked if they would bump me up to one of the other $30 unlimited grandfathered plans as a courtesy for how long I have been with them ('98). Nothing. I finally looked through my data usage and I've never been over 2GB, so I went ahead and took a tiered plan. I hate having to think about it now...but hopefully AT&T will get onboard with DataSense soon and help me out. It's also nice that WP8 has quite a few new considerations for data usage - i.e. picture sync to SkyDrive via wifi.