I was just searching the web (google: can you have two cell phones on the same line) and stumbled across your thread... Finally, someone who thinks like me. I wish they would offer this service because, yes, it would be great to be able to have an "emergency backup" phone in the car at the office, just in case I left mine at home. It happened to me today. I hadn't thought all of the problems through, but your suggestions are great (specifically the phone registration thing). Someday, maybe it'll happen... that would be SO helpful. :)