maznabili

Dear VoIP gurus,

I'm planning for new telephone system. And I got confused when I did research about products available.

My organization is an International School with 65 users - I prefer to say 100 for future growth - I wonder if it is possible to give a piece of advice about which of the systems offers me the following:
1. contract a service provider in the states to get a toll free number.
2. Quota/billing system to reduce un-wanted calls preventing people from over use the system and the bandwidth.
3. IVR/Auto attendant.
4. provide a trunk to our mother organization through the Internet.
5. Fire, evacuation, lock down alarm through the phone system.
6. Supports WiFi phones.
Please, do not forget that it's a school budget, which means that we can not consider Cisco's..

Thank you very much in advance
And please, forgive my demanding nags 'coz I'm still a VoIP novice.