"The defence headquarters has authorised the restoration of GSM (Global System for Mobile Communication) services in Adamawa state," a statement said.
The phone blackout remains in place however for two other states in the region, Borno and Yobe.
All three were placed under a state of emergency in May ahead of a sweeping army offensive against Boko Haram Islamists, with the military shutting down mobile networks to block the militants from communicating.
The army said the phones could be turned back on in Adamawa given the "positive indications" about the security situation there.
While details of the ongoing military offensive are to verify, Adamawa is believed to have seen relatively little fighting.
Boko Haram violence has, however, persisted in Borno and Yobe.