The 3CX site used to have a section on provisioning both the FXO and FXS ports on an SPA-3102, the FXS portion is very similar to the PAP2. At the moment I can't find it, it may have been removed as they consider the devices "no longer supported". If you are doing the provisioning manually you can get the basics from most other Linksys device How-to's.
http://www.3cx.com/sip-phones/cisco-spa501g/
Since you are using it remotely, you will probably want to be sure that STUN is enabled. Where (what type of router you are behind) and what other, if any, SIP devices may be on the same remote network, will make a difference in how you provision the ATA.