Linksys SPA-3102 and another model Linksys SPA-2102 - whats the difference?

2102:
2 FXS Ports
1 WAN Port, 1 LAN Port
SIP + G.729, Auto-Provisioning
http://www.voipsupply.com/spa-2102

3102:
Ports: 1 FXS + 1 FXO + 2 Ethernet
Supported Protocols: SIP
http://www.voiplink.com/Linksys_SPA_3102_p/linksys-spa-3102.htm

harbor235 ;}

I will be getting a RV042 (vpn router) and hooking it up to voip for the first time (Im new to voip)

There will be two seperate lines / two numbers.

2 FXS Ports ?  Are they the phone rj11 ports for the phone?

1 FXO ?

Which one is better?  

Any pics where the ports are visible?
 

Why would this viop adapter have a "fxo -  is the outside line"  I understand hooking up to two external lines.  
 

?? There is one FXO which is the outsid ePSTN line, there is only one on the 3102 ans the 2102 does not have any, it has a WAN and LAN port for ethernet. One is for using VOIP the other 2102 does not haave any FXOs

harbor235 ;}