Callum9432, the part about the texting is correct but not for phone calls in general.
I haven't experienced it myself but I have seen people post about how they have had their Sim call a townie in TS3 only to then see that Sim walking down the road with no phone in sight whilst the call is still ongoing.
That's one of the reasons that some players, and myself, were surprised to see that sending a text actually required the Sim receiving it to look at the phone.