I've got my mobile number on my cats' collars, as if one of them was missing I'd be out looking so the landline number would be no good! I got special collar tags saying that they're chipped when I upgraded to Petlog premium, so those are on their tags too. I understand why some people wouldn't put their phone numbers on their cats' tags, but when my Matilda was knocked down, it was witnessed by a lady who immediately got my number from her tag and rang me. It could have been a long time before anyone would have found the body and scanned it for a chip, so I'm glad my number was on the tag.