With some older cell phones, you can connect them to a computer and use them as a Dialup/FAX modem (to connect to a dialup ISP for example). I have been trying to find out if this possible with Android, but all my searches end up with people looking to share their phones Internet connection with their PC. This is NOT what I'm looking to do. I'm wanting to use Hyper-terminal to have my phone place a call to a PBX, so I can make changes to the PBX remotely.
As I already expressed here, your stock Android phone cannot be used as an AT modem. - There isn't even a serial connection built in.
Question: How is the PBX controlled anyway? Does it implement an "analog" CSD modem, like FAX machines use(d) to?
In that case, you'd be completely out of luck since GSM/UMTS/... data transfer works quite differently.