I guess I'm a Luddite.
I use a spirex pocket notebook and carry 2 biros.
The batteries never go flat, thieves don't want it & the files never get corrupted.
If I drop it in water it'll dry and the info in it will still be accessible.
I always write the date including year at the start of every entry. I've got a collection of notebooks covering the last 6 or 7 years.
My 5 year old mobile phone has about 100 contact name and numbers in it. I keep a laptop in the van with reference info and access programs in case I need it.
I think PDAs are an over priced potentially fallible status symbol. Most mechanics I know have large thumbs that don't take kindly to small keyboards.
Of course I could be wrong