Hello,
I am a VoIP / Telecoms Consultant with over 10 years industry experience and have worked with Asterisk since 2003 and therefore very familiar with Asterisk (please check my profile and feedback). However, if you are looking for a stable Multi-tenant Hosted PBX platform then based on my experience my recommendation is a Multi-tenant PBX system based on another opensource project called "Freeswitch". It is more scalable and was built from the ground up by some of the original Asterisk developers who designed the system avoiding many of the mistakes that were made with the original Asterisk development.
I have been building systems with Freeswitch for about 4 years now and therefore can provide you with a Hosted PBX system with the following features: Auto Attendant (IVR) Ring Groups Call Forwarding / Follow me Call Queues Call Conferencing (Audio) Call Recording Call Blocking IVR / Auto Attendant Enhanced Voicemail ( *97, Voicemail to Email, GUI) Auto-Provisioning of Telephones (Cisco, Grandstream, Linksys, Snom, Yealink), Call Recording additional Storage required Telephone Directory with Dial by Name Multiple registrations from one account and many more...Best regards, Errol