Conversions of radio mic receiver
Like everything in engineering the answer is...
it depends.
It depends on the type of receiver you have and the type of cell phone signal you want to pick up. Cell phone signals are modulated, digital (discrete constellation), and encrypted so even if you picked up the signal, you would still have a lot of work to do decoding and deciphering it.
It's also (very) illegal...
...in most parts of the world.
In the United States, you would run afoul of, not just the FCC's communication licensing restrictions, but also the criminal and civil codes' restrictions against invasion of privacy and unlawful search and seizure.
This is still considered wire-tapping/evesdropping even though there are no physical &quot;wires&quot;. The law makes no such distinction. The legal standard is actually a &quot;reasonable objective expectation of privacy,&quot; a burden that encrypted, privately licensed, cell phones meet.