How can I check my iPhone upgrade eligibility?

So you're interested in picking up the next generation iPhone but you're not sure exactly when you are eligible for a free upgrade. Sometimes carriers will even let you upgrade before the end of your two-year contract if you pay an upgrade fee. To find out if you are eligible for an upgrade:

For AT&T upgrade eligibility dial *639# on your iPhone Keypad and touch Call. A text message will be sent to your iPhone detailing your eligibility.

Verizon Wireless users must check a special website to see their current upgrade eligibility.

Sprint subscribers can go to the main Sprint website and click the 'Upgrade now' box at the bottom of the page. Entering your zip code and phone number will reveal current upgrade pricing for your account.