[Asterisk-Users] Hardware sizing

[Time Bandit]

Hi all,

I need some help/guidance on writing the specs needed on a project
that will be scaling up to 10,000 users.

I will have some T1's to provide PSTN connectivity, and all the users
will be SIP and/or H323 phones. Services offered will include
conferences, voicemail (20 megs per users), etc

Should I use SER in front of asterisk to handle the SIP load ?

I think I should put the voicemail server and conference server each
on a seperate box.

What kind of hardware would be preferred ?  dual-Xeon or Quad Xeon ?

What about redundancy ? 

What solutions can I look into for this ?

Any help appreciated. Any link and/or documentation.

I search with google but didn't find relevant informations. Maybe I
just didn't put the right terms in the search box.

thanks