Have a Dell Streak 7 that not too long ago had the option to bill apps to your T-Mobile bill. (Never bought any though - but the choice was there.)
Recently downgraded my plan from the 10GB to the 5GB and now that I saw an app I wanted to buy, I was going to put it directly on the T-Mobile bill and I am no longer given the choice, only for my credit card.

Any ideas what might be the problem? Could it be the plan downgrade? I'm no a 'value' postpaid account.