Cell phones can from time to time send rather powerfull pulses (e.g. to synchronize / reconnect to base) - enough to be audible with some audio gear.
This was a big issue with GSM, but I haven't noticed audio artifacts with 3G and higher cellular technologies .... although that could be my hearing getting worse with each new generation of cellular technology 
You will get artefacts with all pulsed radio systems, i.e. non-CDMA systems. It will audibly be worst with a TDMA system where the pulses are in the audio band, e.g. GSM at 217Hz.
Equipment has been forced to accommodate such pulses, by better shielding and/or electronically filtering out offending pulses (e.g. a 217Hz notch filter).
Obviously older equipment may be more susceptible, since that threat was never envisaged.
In the land mobile radio world there is also TETRA and DMR. Both are timeslotted and the handheld terminals can have output powers between 1W and 5W.
So far worse than what GSM ever had. Thankfully these are rare.
Unless your sensitive equipment needs to exist in a place where there might be users with those close to it.
Say folks from various public safety agencies.
As for cellphones in general.
I was once characterizing the noise performance of some low noise amplifiers and binning op-amps based on their popcorn noise.
Could not have a cellphone or a bluetooth speaker in the same room with me.
Read a decent amount of books while waiting for individual measurements to stabilize.