Ahhhhh VoIP, now there is a subject any self-respecting Sudo Masochist can spend long fruitless hours tinkering with !!!
I have a VoIP setup in my home/office. Parts of what I planned work, others do not.
I am surprised because I would have thought that what I am trying to do would be a relatively common requirement, with some decent documentation, but after many different attempts, I am still not sure if what I am trying is either conceptually impossible, or just unlikely to work because of bugs in the services and hardware that I use.
I have one PSTN line coming in, I have had this number for over 30 years, I do not wish to change it, it must be handled properly. Due to the mess that is the UK's telecommunications industry, it is not viable to port the number away from British Telecom, so I have to carry on paying them through the nose, just to be able to have calls coming in on that line.
I have accounts with 3 VoIP Providers, who between them give me the ability to make very cheap outgoing calls, a range of addressing schemes on which to receive incoming calls, voicemail that arrives via email, smart routing to the cheapest provider etc. etc.
The problem lies in merging the two.
I have a good quality ATA, a Linksys SPA3000. It can bring incoming PSTN calls into a VoIP network, and make PSTN calls from a VoIP network.
I have a good quality VoIP handset, a Linksys SPA 941, good build quality and physical controls.
What I'd like in the office, is to have one phone and one voicemail account, regardless of where the call originates from, or how it got to me. If I am out I need the whole lot to go to my mobile.
I am so close to getting this working, but the last part of the puzzle is still tantalisingly out of my reach ......
When a call comes in on PSTN, the SPA3000 is able to pass it through to one of the extensions of the SPA941 (also I can call out through this extension to the PSTN line via the SPA3000). What I cannot make work is to have the call forwarded to my VoIP voicemail box if it is not answered. I could make it go to practically any other voicemail box or phone in the world, but not mine, because the phone is registered to that account to be able to receive Message Waiting notifications, plus make and receive calls from that account.
You will not find this kind of detail in the glossy brochures ......
The only way I have found to make this work, and beleive you me, I have tried many, is to have calls coming into my office via PSTN, routed by the SPA3000 out over the net, via my Voice Service Provider and back to the SPA941 in my office.
I have the bandwidth for it, but it is a totally ridiculous way of working IMHO.
Part of the problem is the complexity and adaptivity of the technology.
The web configuration of Sipura products is the biggest html form I have ever had to use, it has no validation and the documentation is very poor (there are many parameters not even mentioned in the admin manuals).
The Voice Service Providers do not have Tech Support, they have online forums. In some it is rare to see any posting from an employee that is not a product or press announcement. What you do find is sporadic, often contradictory information from well-meaning but equally confused co-users of the service, each of whom are trying to set something up that is different from you.
A lot of what I hoped I could get working, works fine.
It is frustrating though, not to be able to deal with the last few details.
So even though you do not have to use the 'sudo' command much, I designate VoIP a fully-fledged Sudo Masochistic occupation :)