Question : SMB VIOP Solution

I am a very small computer business with only a few employees.  I'm looking for a low cost VOIP Solution with the following considerations in order of importance:
1.  Software based, running across a 2003 Enterprise Server network on XP, Vista, Win7, and windows mobile devices.
2.  Quality of voice transmittion and sound clarity
3.  Voicemail with multiple boxes (1 for sales, 2 for support, ect)
4.  1-800 capability
5.  Integration with MS Outlook 2007 and/or Exchange 2007
6.  Remote (Internet and phone) access to voicemail boxes
7.  VOIP Access through public hotspots on Windows Mobile

Answer : SMB VIOP Solution

I agree with using Asterisk or Trixbox but that will not work on Windows.  Freeswitch will work on windows but it doesn't currently have any open source user interface that is "ready".  You could check out the 3CX Phone System if you really need it running on Windows.