Your question depends a lot on the number of users and volume of mail. At minimum you will need a server with a 64bit processor and you will need to be running the 64bit version of Windows Server in order for Exchange 2007 to even install. At minimum a RAID1, but except for the smallest of installations a RAID1 for the OS (and logs) and RAID5 for the information store (exchange).
I do not use SMS so I do not know the answer to that. Most of my clients use windows mobile phones and the exchange connector (active sync)
Thanks, the number of users would be 100 at present exceeding to max of 250.
Also is there any link that i could refer to for installation details, also is one static IP enough,
What stuff i need to verify before implementing the exchange.
Have a look on the microsoft site as it will give you a pointer on how much memory on average per user, with Exchange 2007 it is 64 bit only to utilise more memory, the 32 bit version is for test and Dev or management console only.you need to be looking at around 8-12Gb for your mailbox machine, if you are going to look externally at say OWA (outlook Web Access) then another box would be required to place in your DMZ as a client access server, this will require not a s much but a similar amount of memory as it now does some of the porcessing that the backend servers used to do pre 2007. with 2007 there are 5 roles which you really could do to understand to help with your implementation, the main server can do all 5 roles but see how you get on.
As far as drives and Raid, I agree with above apart from dependant on how you plan to
use the log files, Exch 2007 log files are 5mb each and will dependant on use grow to many many files, you could store them on root partiition (Raid 1, mirrorset) if you dont expect to get much logged or backup regular or store them on their own spindles.
Hope this helps