Magnets distort cathode ray rubes (CRT's). It can be reversed by degausing. You can easily see that effect.
Magnetic fields affect magnetic tapes (VCR, cassette etc). Magnetic fields could affect the cell phone on a temporary basis. Might affect range. Magnetic fields affect hard disk drives.
There is a non-volitile memory that is magnetic based, so it could affect that.
Anything that has transformers or coils especially for coupling can be affected such as a speaker on a cell phone.
In general, the effects are reverseable unless there is data stored on the magnetic media.