I've had great success with the AT&T microcell improving cell phone and data coverage in my home office. Without it, I get one bar of AT&T service - on a good day. With the microcell, I get a full 5 bars. However, I recently obtained an LG Quantum WP7 (AT&T) for testing and couldn't get it to recognize the microcell. I tried multiple times to add the number to the whitelist and even swapping out sims and trying different phones but I couldn't get my new number to work. I called the AT&T help desk and after troubleshooting unsuccessfully for 30 minutes, they recommended that deregistering the microcell and re-register it which did the trick. Now all of my phones, including my new LG Quantum Windows Phone 7 recognizes the AT&T microcell and get a full 5 bars of service. This will help greatly with my testing efforts.
On a related topic, Ed Brill announced on his blog that IBM is exploring offering Lotus Domino support for Window Phone 7.