Cynically speaking, obscurity in this case is good for security. Because not much companies can afford to reverse-engineer the whole stack and create malicious GSM software/hardware.
As for competition, there's enough of it in the hardware cell-tower market. They are produced in millions, and basic GSM cell phone infrastructure (i.e. no GPRS, EVDO, etc.) is now VERY cheap on per-subscriber basis. Use of non-carrier-grade hardware is quite likely to _increase_ costs because of increased maintenance overhead.
No, the next battlefield will be 4G technologies. They have the potential to uproot established telecoms. 4G phones will be simple IPv6 nodes, and calls between them are going to be simple VoIP streams over data network which can be (by design) transmitted over the WiFi and public Internet.
PS: I worked as a network architect in a small cell-phone company.