Telephony (in VoIP) is mostly C/C++, then with a smattering of scripty stuff to tie it together in the UI. PHP, Perl, Ruby. Bigger places use Java and maybe a few on .NET. WebRTC seems hot, and the frontend would need JS in a browser, but in the backend... Despite Erlang supposedly being "made for telecom", I've not really seen it be used much. (Yes I'm aware some big switches use or have used it, just haven't seen it in VoIP much.)<p>If I were in the position of trying to get remote work in telephony, I'd start learning the popular open source packages in use (Asterisk, FreeSWITCH, OpenSIPS), read up on protocol SIP (SIP Illustrated is a good course, includes an annotated RFC) and get your name out there in the community (answer questions, post write ups, etc.)<p>There's a range of work from cobbling CRUD apps together around a telephony core, to fixing core code, setting up networks, etc. Telecom has a lot of legacy and complexity, and that means there's opportunity for people figuring it out. I've seen this happen: guy joins mailing list asking super newb questions. Fast forward a bit and now he's billed out as an expert. All self-taught and promoted.<p>You'd also need solid networking skills (which come in handy even in web dev; I'm annoyed/surprised that many "web developers" are unable to diagnose basic network issues with Wireshark). The material in a CCNA course should be a decent starting point, though don't obsess about learning IOS management.<p>On languages, if you're steady with C (you have a good idea how the machine works), and you've got a couple popular languages learned, I don't believe language will hold you back. Domain experience will compensate, and you can always learn new languages easily enough. Though I'd <i>highly</i> suggest picking up a functional language (I'm preferential to F#) for the much more powerful thinking it'll bring you. Ultimately, I'm unconvinced that picking up a hot language will lead to work in that language (hey, I just learned Go, hire me!). But demonstrating ability will show you off very well. For instance, Rust is hot, a <i>great</i> language, and there's still opportunity for write-ups on "I did $neatish_thing, <i>in Rust</i>", to get a fair amount of interest.<p>Otherwise if you really just are trying to bid on random contract work, others said it: adding the JVM/Java keyword is probably the best way to increase reach.<p>Edit: With 17 years IT, when you add programming to the mix, you now have the very hot "devops" buzzword which seems to be very popular.