I dunno, I feel like the title may eventually come to mean something. If the "bells" are the TARDIS's phone ringing, then somebody/something had to make that happen. It wasn't just a random shop girl that gave Clara the phone number; something set this all in motion.
Well... yeah, obviously.
Some random shop girl wouldn't have the TARDIS' phone number and the script wouldn't have drawn such attention to it if it wasn't going to be resolved, nor would it specifically point out we don't know what the person looks like for now, meaning it's probably someone we know, IE River or Rose or someone else.