Just found this: Is it possible to virtually emulate a SIM card and make it work on a mobile phone?
SIM card basically carries authentication information to make the required connection with the network. So, to be able to connect to a network in the name of SIM you don't have, you have to have the information which the SIM carries.
Once you have this, you have to tamper with the phone's hardware(and/or software) to get the information it is expected to collect from the SIM from somewhere else.
Since, the interface between the SIM and the phone is standardised for any given technology, it should not be impossible to mimic this, using a combination of hardware and software. But, such a system is readily available? I haven't heard of.
It seems it's possible if you're genius enough to understand and implement how the interfacing between phone and sim card is done, because on the basic level, a sim card is nothing but a storage device holding access codes and data (you may just virtually store this info and emulate/read it like there's a sim card).
But as far as I searched, no one has done it.. And also, as @Andrew commented, you need appropriate radio hardware to make telecommunication even if something like that hack is accomplished :)