We have a "smart jack" installation that connects to our router. The cable going from the smart jack to the router WAN interface seems to be a CAT5e cable with RJ-45 connectors at both ends.
Most network diagrams in training materials represent T1 Frame Relay connections as serial links.
Is the CAT5e cable wired different than a straight-through configuration? Is the port on the WAN port a T1 DSU card?
Yes is wired different and also the impedence is different. That is called a T1 cable with RJ48c connector.
The WAN port on arouter sometime is T1, sometime CSU/DSU, sometime something else. There is no fixed rule.