I wonder why they are not supporting these anymore....
http://6200networks.com/2008/07/14/12415t-is-last-cisco-ios-t-release-for-select-cisco-router-platforms/
12.4(15)T is the last to be supported for these models:
So what platforms aren’t supported exactly? Well here’s your list:
* Cisco SOHO 90 Series
* Cisco 831, 836, and 837 Series
* Cisco 1701, 1711, 1712, 1721, 1751, 1751-V, and 1760 Series
* Cisco 2610XM-2611XM, 2620XM-2621XM, 2650XM-2651XM, and 2691 Series
* Cisco 3631 and 3660 Series
* Cisco 3725 and 3745 Series
* Cisco 7400 Series
* Cisco AS5850 Universal Gateway