A really neat way to accomplish this is to purchase a "TAM B" Telephone Access Module from Bogen (Ramsey, NJ). All you do is program an analog port in your option 11C (I like to assign 7243 as the DN - this S P E L L S out PAGE).
Then you cross connect the TN to the T&R connections on the TAM B, and then run a cross connect from the paging T&R connections on the TAM B to the amplifier of the page system. Now any phone (digital or analog) can dial the page DN 7243 and...you can program auto dial keys to your digital phones for one touch dialing access to the page. PS... If you want to restrict access to the page system you will need to cross connect the TAM B to a Trunk port. If you are going to use a Trunk port you will need to purchase the power supply for the TAM B from Bogen, if you are going to use the analog port configuration, no power supply is required.