AT&T today said it plans to switch off every last bit of its 2G cellular network by January 1, 2017, a move that will require migrating customers to modern devices and building out 3G and 4G networks. That means some people will have to upgrade their phones, because AT&T said the spectrum used today for 2G services will be reallocated to its 3G and 4G networks.

About 12 percent of AT&T's postpaid customers (that is, the majority of you who don't pre-pay for service) are still using 2G phones, AT&T said in a Securities and Exchange Commission filing in which it discussed its plans. More than one-third of postpaid smartphone subscribers use 4G devices (on HSPA+ or LTE networks), while the rest are on 3G. Even those phones may sometimes have to rely on the older GSM and EDGE 2G networks in congested or remote areas, however. But the network upgrades should hopefully be good for everyone except those people who really, really want to keep their ancient phones.

"Throughout this multi-year upgrade process, we will work proactively with our customers to manage the process of moving to 3G and 4G devices, which will help minimize customer churn," AT&T said in the SEC filing.

AT&T said it is facing "significant spectrum and capacity constraints" in certain markets, which could affect quality of wireless voice and data services unless the Federal Communications Commission can "make new or existing spectrum available to the wireless industry to meet the needs of our subscribers." AT&T said yesterday it's getting more spectrum licenses as part of a purchase of NextWave Wireless, but today's SEC filing shows that switching off 2G services is a crucial part of its plan to set aside enough spectrum for 3G and 4G networks.