Bluetooth via cell phone is not an option for my system.
Don't see it would be necessary given the remote keyfob is already hands-free and about 5% the size of a phone.
So what would it bring of benefit to have it?
Regarding the previous questions about back-up, at least to my personal knowledge I have never had ANY system failures, other than two who managed to flood them with water.
I don't know of anyone (at least no-one has informed me) of a failure that required re-connecting the OEM key-switch, but it's a re-assurance (I suppose) to know that you can if need be.
Remote batteries last about 2 years - I recommend to replace them annually which is just good practice given they are quite inexpensive anyway.