This is already the case in my game, and I have not installed AL yet. The only real problems it causes is that if I exit while the sim is on the cellphone and there are no other phones in the house, other sims can't call them. This is easily solved by just canceling the talking-on-phone interaction before exiting.
No, that's not it. They reach into their ass to answer the cellphone and poof, it's gone. The wall phone will still ring and can be answered, but the cellphone is no more.