Advice on web solutions, please

I am hoping to build an online game platform that will enable umpires and authorised players to talk to each other via VoIP, plus send/receive text messages. There is no need to connect with handsets, communication between PCs will suffice.

The software needs to be Open Source as I will want to modify the code; it should also be web-based so as to minimise the deployment/support issues. Asterisk may be the foundation for a suitable service but I am not aware of any web clients, though I must confess that I have not looked at the code yet. There may be related packages that I could use; sipml5 looks promising for example but it is new and I know very little about it.

Please note that I am fairly new to the VoIP world but I do have extensive programming experience; my preferred language is Python but that is not suitable for inline web development.

Thanks …