Trying to track down the nitty gritty of specifications of End-Of-Sale equipment can be a pain. Thanks to a post on Netpros, I found the info I needed. 2600XM series Routers have 16MB of non-removable Flash, so if you want to max out your 2611XM with 48MB of Flash, you just need a 32MB simm. You can find info on the part numbers and installation here.