Survivor Bayo Osho said they were at work in the Airtel building located near Mallam Kalto Square in Sabon Gari when two suicide bombers drove separate vehicles into the premises.
According to the survivor, the first car was used to force the gate open and the driver came out and exchanged gunfire with the security personnel before the second one, laden with explosives, drove in. The explosives went off and sent billows of flames and smokes into the air.
Officials from Airtel, one of the three biggest mobile phone service providers in Nigeria, were unavailable for comment.
A local news website, Street Journal said four persons died. But it was not immediately known if any civilians were killed. It was also not known where the casualties took place.
Islamist group Boko Haram, notorious for shootings and bomb attacks across north and central Nigeria, has in the past targeted phone companies, accusing them of cooperating with the security services.