So far only very short, there is much more to add.
I refer to the switching power supplies, not the old-style heavy ones using a transformator operating a Mains frequency directly.
Usually there is a specification like "OUTPUT 5.0 V 350 mA" together with DC-symbol on them. One might reasonably expect a stable voltage output. WRONG! For both Siemens and Nokia I found voltage depends heavily on load, starts at approx 8 V for light loads below 1 mA, and goes down then. This of course might kill electronic circuits if you carelessly use such Mains adapter for a more general purpose (power supply for lab experiments).
My personal impression: The mobile phones are designed to fail after some years, even when not being heavily used, even when being off most of the time (charged Battery installed, means some parts are powered). So far did no in-depth analysis what failed. Signs were (despite new Batteries):
(myself and parents supported by me)
... still the right size - you have something in your hand!
Phone and voice recorder, for me. Music player for others.
can much more, but with me for SMS writing.
It does not run on Mains adapter directly. It will charge and discharge the Battery instead. Using it contiguously as Data Modem wears Battery in a very short time, means a few days or weeks.
If you just want phone calls, some SMS, and a good flash light. You get a permanently visible digital clock for free (b&w LCD is perfectly readable without backlight).
Unfortunately, color LCD needing backlight ...
--- Author: Harun Scheutzow ------ Last change: 2011-07-12 ---