AT&T says that if its deal to buy T-Mobile USA goes through, T-Mobile subscribers with "3G" phones will need to replace those to keep their wireless broadband service working.

AT&T Inc. on Sunday said it had agreed to buy T-Mobile USA for $39 billion. If approved by regulators, the deal would close about a year from now.

AT&T said Monday that it in the year after the closing, it plans to rearrange how T-Mobile's cell towers work. The spectrum they use for third-generation services, or 3G, will be repurposed for 4G, which is faster.

That would leave current T-Mobile phones without 3G. They would need to be replaced with phones that use AT&T's 3G frequencies. AT&T said it had factored the cost of replacement phones into the total cost of the acquisition.