you have read this thread, i assume ?
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.