If the T1 handoff is Ethernet (either copper or fiber), then 3750 will do. If the T1 handoff is non-Ethernet (tradisional T1 off Smartjack) then you need some device (typically a router) with CSU/DSU modem, either external or internal.
What you can do is to confirm with your ISP or telco to find out what kind of handoff they provide. Just because it looks like RJ-45 cable, doesn't necessarily mean it is Ethernet handoff.
You also need to confirm with them what kind of network topology you deal with. Confirm with them how your network (or your device) participate in OSPF and IS-IS.
