I just got an ATT 3G Microcell for home, since our service is intermittent, sometimes so bad I can't send an SMS message successfully (although at times it works fine). We live in the mountains, and have several different poor signals to bond to, so that's probably why it is variable.
In the store, they checked my phone number and said I couldn't activate a Microcell on my account, since it's a Netflix corporate account iPhone. However, my wife has an iPhone on a personal account, so I used that as the activation account.
However, when I tried to add my own phone number to the Microcell's whitelist of up to 10 numbers, I got this error message
"FTC309: invalid subscriber information found" - which got no hits on Google, however after this blog post it should get one..
So the website told me to call the generic ATT support number. After a few short waits, a very polite first level support guy (who had probably never heard of the Microcell before I called) found a well informed business support specialist who was able to confirm that the error code was due to the Microcell only supporting consumer accounts. She agreed that it didn't make a lot of sense, found that they had been running a trial of corporate accounts a few months ago, but didn't know when/if it might change. She forwarded me an internal support document that discussed the limitations of the trial, including the lack of corporate support. Although it does say that it supports all ATT 3G devices.
I installed it anyway, it takes a few hours to set itself up the first time. We will see how well it works for other iPhones, meanwhile I will just have to use Skype to make calls and send SMS... If it doesn't work out I will take it back.
------- Update -------
I contacted the corporate account support team via work, and they over-rode the system to add me to the Microcell. So my corporate account iPhone is now working fine with the Microcell. They are investigating further to see if they can make this a more general fix for other people, but if you are in the same situation as I was, you should be able to escalate to support to get it fixed.