Mobile telephone carriers must allow customers’ competitors to connect to their networks, and they must make roaming available to competitors for a “reasonable” cost, the U.S. Federal Communications Commission said Tuesday.

Reacting to complaints about large carriers charging heavy roaming fees to customers of smaller competitors, the FCC voted to require that mobile carriers provide roaming services on a nondiscriminatory basis. Providing roaming connections is an obligation of commercial mobile phone carriers, the FCC said.