I had good luck getting United to match my AA Platinum status.

I emailed the following to [email protected]:

1) Scan of my AA Plat card (front only)
2) Screen shot of my January 07 statement (With not much actually on it).

Took 1 day, and they updated my status and sent a welcome email.

I find this more convenient then sending a fax...so thought i would share if someone has not already.