We are currently running 2 Avaya IPO 500 across 3 sites all coming through 20 Lines of ISDN30. Looking into 5 Lines of SIP trunking for redundancy at a remote site. Also have Voicemail Pro 7 installed with SMTP backup to remote site. Runs really well, easy to manage and licensing is also clear. Also setup Campaign Manager on the voicemail server to reduce calls for the attendance team in the morning so parents can choose to go through an automated service.
Dont know if this is of any help just a few ideas
