This is taken from my Sprint on a 2.1 ROM with working Arcsoft under WspHeader2. The key that is of interest to me on here is the Accept = MDN, and the X-MDN where my phone number has been blacked out. The phone number format in the value field had the 1 in front of your 10-digit phone number.
I am also wondering if we need to be using the hmac-md5-key as I know when certain roms couldnt use Sprint bloatware we were getting an error saying that the md5 digests do not match. Perhaps this is used in authenticating to their server. The above picture was from WspHeader in the registry under Arcsoft for Sprint.