Apple

Unless it's a hardware failure causing spurious emission, it just means that transmit power has been reduced in software. Practically, this will reduce the range at which you can communicate to the cell tower. The cell tower reception should remain nominally the the same strength and the same speed, but you will have a reduce range for towers to which you can reliably connect (i.e. dropped connections) because you can't tell the tower you're listening. Also, your upload throughput will be lower at a given distance from the tower as your distance from the tower increases beyond a (now smaller) full-connection-strength radius.