PDA’s or PDAs?

Which is correct?
Anything that promises to keep operating costs lower is likely to spur the market for smart phones and _____.
a. PDA’s
b. PDAs

Answer: b

Explanation:
If you follow AP style, the only case that calls for an apostrophe to pluralize is that of individual letters, as in”Mind your P’s and Q’s,” for example.

Ryan’s linguistic blog lists this horrifying example of misuse found online:

“Hey guy’s. I was wondaring do you love dog’s or cat’s? I like dog’s!!! Please say dog’s. Dog’s rock!”

Well, at least s/he was consistent.