I lost 5000 Marriott points last year when I switched to AT&T because I didn't keep them for 30 days. The offer said switch and you get the points (nothing about minimum time you had to be with AT&T). When I called to complain about not getting the points, they told me that since I switched back in less than 30 days I couldn't get the points (even though I had paid for a 30-day period). Called Marriott and was told in March that they had spoken with AT&T and that they were "making an exception" and the points would post within 4 months! End of this month is 4 months and I haven't seen the points yet. August 1 another call goes to Marriott - I feel more confident about getting the points if they fight this battle with AT&T.
Now with MCI (and pretty happy). I too have put a block on my long distance service. I love the idea of cashing the checks and not switching. I have a check from AT&T right now and may do just that for the aggravation they put me through.