cell phone number linked to two or more phones

Question

What are the technological reasons, if any, that prevent cell phone networks from allowing one number to be linked to two or more phones? Say you have a larger phone for daily business an a small one to carry around on trips at night etc.

Answer 1

It is the simcard which limits that. Each simcard has a unique serial id which is then linked to a telco number. Put those two together and you hav a single unique id worldwide.

Maybe there is a technology which can allow to link many simcards to one service provider. Bt then that will defeat the uniqueness of a number and maybe might raise security issues and number clonning problems.