osmocomBB purpose & GSMs

Hi all, I'm new in these forums and osmocomBB. I was wondering, how does osmocomBB work. install 2 packages, one on the phone and the other on a PC Host? And then you are able to call/sms and anything a GSM phone can do? And you can change the GSM protocol/stack if you want to? So pretty much your PC becomes a GSM terminal? also Are there any simple guides to setup the whole thing? Ahmed