mobile-phones (which was merged with
cellphones as noted).
Only one question tagged with
smartphones could be argued to deserve it. People seem to use these tags when they have a question about a phone, rather than a general question applicable to many phones, which is silly.
tablet is a little better (probably because there are fewer of them) but we should keep an eye on it.
I didn't seen more than one or two
cellphones questions that were actually about hardware, so I don't think merging them under
hardware is necessarily a good idea.
I am in favor of blacklisting mobile-phones and cellphones. Matthew is right: If the phone functionality in question is calling, calls is the tag to go. And for everything else, mobile-phones and cellphones is to broad and inaccurate.