Most problems with pager communications seem to be caused by modem initialization strings. The modem must have the "interface to modem" and "modem to distant end" set to the same baud rate, either 300 or 1200 baud. The modem must have "echo" disabled, "command textual responses" enabled, must return standard Hayes compatible responses, and must accept Hayes compatible commands. The system must be tested at 300 baud.
Once, you've established that the pager works, you can change the baud rate. Modems that return connection information other than "Connect ..." must have the extra connect information turned off. Modems that lock interface speeds must have that option disabled or locked to the desired connect speed (300 baud).