Looks like the 2691 was 3 WICs and a NM port which I believe would support 2WIC, 2WIC 1FE, or 2WIC 2FE. So you could have up to 5 T1s on this setup. Are you using the WIC 1DSU-T1 card or the WIC-1T card? There is also a 4 port or 8 port IMA card that will work in the NM on the cisco 2600...