BIS Outage Caused by Move to BES
 

Yesterday from about 10 am EST I was not getting any emails on my 9700. Then when I went home and was on Wi-Fi the messages started coming. Today no messages again once I left home so I called T-Mobile. The tech asked if I was using BIS or BES? I said BIS, he said, "hum, that's strange - that berry is listed under BES here." He changed it back to BIS and resent my service books and now I'm getting messages again.

So my question is - how could I have been switched from BIS to BES? I did nothing yesterday to the Berry except a battery pull to try to fix it when I stopped getting messages.

You weren't switched from BIS to BES. Your data plan was. There's nothing you can do (other than call and request it) to change that. It's done on T-Mobile's end.