These are not PSTN phones. These are run by software that is burned onto a EPROM located inside the phone. Depending on what access the software gives depends the service we can take from it. All these thigs depend on the AT commands that are fired. Since the AT commands are restricted on these phones (custom manufactured for Reliance) many things wont work. Even things like sending SMS, download the address book etc.
TIP: Try searching for the international version of the same phone that reliance provides us, the features that are provided to us here in India are far too less. Its all a makketting stunt they keep doing cause we Indians are not tech savvy