Using WCL to Manage 900 AP across 300 node MPLS Network

Question

Cisco is recommending we use a Wireless Controller at our corporate office to manage 3 APs at each of our 300 store locations (900 APs total).  I would like to know if anyone has deployed a similar solution to determine if this is a good approach. 
The Corporate office has a DS3 (45Mbps) connection to the MPLS cloud.  Each of the 300 stores has a 768K connection.  Typical network response times range between 20ms to 85ms depending on hops and distance from the corporate office. Store APs would be thin (1131s or 1142s) using HREAP with local switching.  Each store would have its own HREAP group to manage the AP at the store.  Ideally VOIP and local data would stay local.  Auth and Internet traffic would route through the WLC.  There is no local internet circuit at the store.  All Routers, Switches and APs are made by Cisco.  We are using Cisco CME with 79xx phones.  Each Store has 4 each 7921 wireless phone as well.
I am told that VOIP roaming in a store will work if the store is offline (disconnected from the WLC) via local auth to the AP.  In theory this looks feasible, but I have no reference to confirm.
If you have a similar setup I would like to hear from you to learn how well it works and if you had any problems with the initial installation.

Answer 1

Store APs would be thin (1131s or 1142s) using HREAP with local switching.
Firstly, in wireless parlance there is no such thing as a "thin" or "thick" AP.  It's either autonomous or controller-based (sometimes called as LWAP or CAPWAP).  Please refrain from using this term as it will make you sound smart when you are talking to the un-initiated. 
Ok, so you got H-REAP.  This is good.  Now the question is do you have local RADIUS at each store?  If you don't then your store is "useless" if the WAN link goes down because when the WAN link goes down and a new client needs to authenticate then it needs to find the authentication server, HOWEVER, if the client is already authenticated and the WAN link goes down, it's still OK.
Next, Wireless VoIP and roaming.  Presume you have a 7921 with the extension number of 12345 and this is for your branch, say Las Vegas.  Let's say that you went to your Atlanta office.  Guess what, if someone calls you at your extension number of 12345, your phone (currently in Atlanta office) will ring.   (By the way, did you hear about the new model, the 7926G?)
WLC, you'll need to look at the Flex 7500 WLC.  This model will do nothing BUT H-REAP.  How many clients per branch (aside from the 7921G)?
I am told that VOIP roaming in a store will work if the store is offline (disconnected from the WLC) via local auth to the AP.
As long as the WAN link is not down then the 7921 should be able to survive if the WLC is off-line as long as the WAPs are not reloaded after the WAPs lost "sight" of the WLC.