Customer is looking for portable units staff can carry an external device to receive pages from the CTX670 but can not make internal or external calls. Customer site does have wireless capabilities.
The only thing I could think of is interfacing a push to talk radio unit with the CTX.

How many, what range?

You could give them DECT 6.0 phones with page capability that run off an unused CO port.

Some of them go up to 8, maybe more, units off one base that would be plugged into an analog CO. Usually any phone could page.