I always know when I'm about to get a call in my car, because I get
that tick-tick-tick bzz oscillation over my car stereo speakers just
before the phone rings.
Briefly,
In my experience, condenser mics with unbalanced or
"impedance-balanced" outputs are all susceptible to cell phone
interference to varying degrees.
Mics with transistor-balanced outputs, i.e. mics that have the Schoeps
CMC3 topology as a common ancestor fare much better than the unbalanced
mics, but will still oscillate if the phone is near (within a foot or
two of) the cable or XLR output of the mic.
Hybrid mics, such as the Schoeps CMC6's reject this interference better
than the discrete balanced mics.
However,
Mics equipped with output transformers that I have tested are
completely immune to this problem.
The offending phones appear to be CDMA and GSM based and the resulting
noise occuring as a result of the carrier signal coupling through the
cable, causing the active circuitry to oscillate.
Brent Casey
PMI Audio Group
877-563-6335