No, the modern generation of cellphones (GSM 2G), have no problem keeping track of which site a handset is operating. The handset actually monitors a number of sites simultaneously, not only for signal strength but also for available capacity on its site and the handset itself then makes the decision on which cell to hop to. The HLR of the operator (HLR=Home Resource Locator - basically a database which records where the phone is at any time) is updated every time a change is made and charges are made accordingly. If it roams, then the new host HLR is updated and charges go back to the home operator.
The reason they are banned is nothing to do with ability to charge. Think on it, if it can make/receive a call, then the cell operator knows where it is and who's network/account to post charges back to.