[cisco-voip] SRST (in 2821 and 3825) vs. CMM vs. AWG and some survivability design Qs

[Netfortius]

Does anyone have a pointer to features comparison and/or - mostly - personal 
experience/opinions about differences between IP telephony capabilities, as 
far as survivability of remote sites, between the traditional SRST available 
for the integrated svcs routers, and CMMs (for 6500s), as well AWGs (4000s - 
wondering if the 4500s still accept them?!?). Here is the challenge I am 
faced with: planning for VoIP, with all remotes being provided with dual 
2821s (for redundancy), dual-connected to either two 650x or two 450x. We are 
having a very heated debate, in my group (mostly out of lack of complete 
knowledge about VoIP/IPT Cisco products, for any of us), in regards to which 
way to go, knowing the followings:
- all remotes will have anywhere between 100-240 phones;
- our design consists in a cluster of CMs at the HQ;
- we have identified the need for some survivability (of course) for when the 
links between remotes and HQ is not available (no CM for the phones to 
register with);
- my definition of survivability is: remote phones should still be able to ALL 
communicate with each other, and any one of them being able to go "out" via 
PSTN, in case of disaster (of course within the limitation of number of POTS 
lines we will be providing fr each site).

Considering all of the above, I would really like to avoid scrapping the 
2821s, just because of their limited capability in support of phones (48/ea, 
compared to my requirements), but I am also very much inclined to believe 
that the best solution is a 3825/45 w/SRST. Some of the other guys are of the 
opinion that we would be better off putting CMM module(s) in the 65xx (where 
we have them), or AWGs in the 45xx (where we have those).

I would appreciate any comments to the above, or - as stated originally - an 
RTFM link to some product comparison.

TIA,
Stefan