WEB BASED (saas) Phone/PBX/ivr/fax/autoatt based voip-fax-billing solution

Repeat as another project _ Our client needs a Turnkey inexpensive solution. Their website is up, but need the backend as described below. ****** the user interphase has to be current looking... NOT the 90's layouts. **** NOT a calling card business This will be a Web Phone Service Provider. Just Like: RingCentral(.com) and Grasshopper(.com) Client looking a voip solution that can be installed in a CENTOS VPS, where I can offer Voip subscriptions, Virtual Fax and includes a billing system (with gateway integration like paypal for recurring billing). The voip handler must allow me to set PBX and autoattendants for my clients. And of course a small control panel for my client where they can set up basic functions as voicemail, forwards, e-911 address changes, virtual fax, etc. >>>>> If you have samples already working online, please, let me see or test those projects. Experianced only need apply, and will be looking at RATINGS, thank you.