If you want to go Sprint and get the 25,000 Northwest WorldPerks miles, you get 5,000 for switching to Sprint and 5,000 miles/month for the next 4 months. 877-282-6742, must ask for "Sprint SenseDay"
For MCI: Same deal as above, 25k miles with respective partners. The codes & phone numbers are:
Z25A-American, 800-432-3426
Z25C-Continental, 800-256-1474
Z25D-Delta. 800-269-2292