I regularly filp-flop between MCI and AT&T. With MCI, you can usually get 10K miles over 6 months with 5K during the 1st month. Since the initial 5K is the best pop of the promotion, it's okay to switch any time after it deposits. However, I've found that competing (cash) offers from AT&T usually don't arrive until month 4 or 5 -- perfect timing! I have another line that is married to Sprint for the next 11 months because I'm in the middle of the 40K promo for NW. Hope that helps.