I make vehicle tracking devices that use cellphones. That doesn't mean that I know much about how cellphones work, just that I know how to use some features on them.
The way that cellphones communicate with the cell towers is incredibly complicated. Just to give you some idea here are some details on the way that they work.
When numbers are dialed, the digits are not sent separately, one after the other like the DTMF tones on a landline. A data burst is sent with all the dial information.
The frequency and power of the transmission will depend on what tower the phone is talking to. It can change during a call as a call can be handed from one tower to the next.
I am fairly sure the number is encrypted. The voice or data is certainly encrypted.
The phones do not transmit all the time, even during a call. They only transmit for 1/8th of the time, 216 times a second. So there is a burst that is about 570 µs long, every 4.8 ms. If there is another cellphone near, it may be transmitting on the same frequency, but in a different time slot.
The timing of the transmissions from the cellphone is varied so that all the transmissions on one frequency (up to 8) will arrive at the tower at different times. If a receiver is somewhere else, some transmissions may arrive at the same time.
The result is, if you want to get data from a mobile phone, use it the way it is suppose to be used.