Sami,
you have read this thread, i assume ?
http://www.erlang.com/forum/erlang/thread.htx?thread=2660
it really looks like the choice depends on manufacturer to do the sleep thinggy or not. Removing brutally the battery is the worst case, I doubt any phone can bear it.
But frankly, there are so many phones, you cannot find a “common” rule for all of them.
For the clock, the date settings are perhaps stored in the ram regularly. And at startup, the ms will just load the stored date.
cheers
pix