paradoxsm: the 4G systems boxes are not locked, I used a prepay SIM in mine until I got sick of the poor Audio quality.
The SIM's have an applet internally to detect IMEI ranges or certain manufacturer IDI think, the only other thing I ever got it to register in was this old Siemens module. I never tried it in a hacked phone with a changed IMEI. (if such a coveted thing actually existed!)
John, can you confirm if the new Panasonic Cordless model is SIM locked?