We asked a cell phone rep. give our flight department a presentation on their services, products, and also inadvertent useage, (pax), in the air. Here's what he said:
"Big cell phone service providers get pretty upset when you make a call from the air and the call is directed through more than one cell antennae. Causes big problems with their systems."
He mentioned a huge $$ penalty too. Can't remember the exact amount is but $10,000 dollars imposed by the FCC from what I recall.
I'd check into it before giving up on the signal lights. Lost comm procedures were produced and implemented to preclude the need for tower communications anyway and the tower personnel are well trained for this eventuality.
Cell phones are definitely another asset for us to use, but I would only consider it in an emergency situation.