Make them all use a common frequency plan (LO, IF freqs), and be tested to strict EMI standards. That way aircraft manufacturers could effectively shield the internal systems from the known freqencies, rather than the plethora of frequency plans that exist today (different from vendor to vendor, and model to model).
It wouldn't do you much good anyway, since you are so high up you can't stay in contact with a tower long enough to connect a call, or do a proper hand-off between towers to maintain a call.
The better solution might be to make cell phones have an aircraft-mode that uses a small range of frequencies that interfaces with an onboard relay system that routes all of the phone traffic to an antenna outside the aircraft that ties into the cellular/telephone communication systems (a SATCOM link, perhaps?).