According to the AT&T blog, they are changing their upgrade policy adding 4 months meaning your upgrades will have to be 24 months, not the current 20 months. There’s always a few ways around it as they explain:

Today, we’re announcing a 24-month upgrade policy across all of AT&T’s wireless products and services. This aligns device upgrade eligibility with our standard two-year wireless agreement and it applies to any customer whose agreement expires in March 2014 or later.

AT&T will continue to offer a variety of options to best suit customers’ individual needs:

- Purchase a subsidized device with a new two-year wireless agreement. You will be eligible to upgrade your device at the subsidized price after 24 months.
- Share an upgrade. Share an upgrade with another person on your account provided it is within the same device category (e.g. phone to phone, tablet to tablet, etc.)
- Early upgrades. Once you’ve completed six months or more of your Service Commitment, you qualify for partial discount off the full retail price when you sign a new two-year wireless agreement.
- Trade-in. Take advantage of our trade in program. And, for a limited time, when you trade in your current smartphone (three years or newer and in good working condition), you could receive at least $100 off the purchase of a new smartphone.1
- Purchase a device at full retail price. You can pay full retail price for a phone anytime without a two-year Service Commitment.
- Bring your own device. You’re welcome to bring a compatible GSM-capable phone to AT&T and sign up for service without a Service Commitment.
- You can go to http://att.com/wireless to check upgrade eligibility or dial *NEW# (*639#) from your wireless device to receive a text with your upgrade eligibility date.