You don't need the Nokia ORB to communicate through a TCP/IP from your application module to TCP/IP connected parties. You can use whatever standard C/CORBA or X/CORBA implementation, where X is your favorite language. Probably all of them support IIOP on the OS TCP/IP stack, independent on the underlying transports, be they PPP-over-modems or Ethernets.
On the other hand, if you want to communicate through the Nokia GSM Connectivity Terminal, sending CORBA calls through the M2M System Protocol, you need the Nokia C ORB.
If you are looking for system, that transparently connects you with a TCP/IP over the GSM network so that you can use IIOP and not even know about whether there is a GSM network (and not do any optimisations, bearer selection, text messaging etc..) or Ethernet, you can use the Nokia Terminal as a GSM modem in the embedded device, running PPP over it. Then you don't use the Nokia M2M Platform or the Nokia M2M Gateway. You should then use your regular modem pool (Network Access Server) features for authentication.