Virtually every paging system that uses touch-tone can take type-ahead. If you have a dial-modem (I got rid of my last one more than a decade ago), you can use that to dial out, pause a second or so at appropriate places, and then send the digits. The easiest way to do this is with Hayes command sequences.
However, most paging systems now take eMail input, so that’s a much easier option.
Sheldon Linker (email@example.com)
Linker Systems, Inc. (www.linkersystems.com)