All my animals have the AVID chip, I don't remember having to do any extra registration for them.
My son lives in TX, I live in CA, and while visiting him last year we took a lost dog into the local animal shelter. I refused to leave until I knew if he was chipped or not (if not, I think my son would have had himself a new pet). He was, whew! The gal at the shelter said if they're chipped, they can read it regardless of the manufacturer (I'm assuming AVID isn't the only chip on the market).