To answer your question, yes. There are multiple ways to integrate with a Paging system, but it all depends on the paging system. Valcom and Bogen can be integrated by using Analog FXS or Analog FXO. They also make a version of paging system that will integrate via SIP.
If you are looking for something that will allow you to page over the phones as well, then you will need to look at a full VoIP paging system such as Informacast as Manish has described. They also have an LPI (Legacy Paging Interface) that will allow you to integrate with analog paging systems so that you can paging to both phones and overhead speakers if not IP based.