I completely missed the announcement of this, but Web21C is a series of APIs for BT’s 21st Century Network, the next-generation IP-based telecomms network that’s being rolled out.
It’s a number of APIs to core 21CN services - SMS, voice calls, conference calls, location, authentication and so on. They’ve created an SDK which allows these services to be embedded into web apps, as well as test environment - in a particularly nice touch, there are seven virtual SIP phones for testing, each one with it’s own particular quirks. And to distinguish each one from the other, they’ve been given names from Snow White - so Happy will answer the call normally, but Sneezy will accidentally disconnect the call after 10 seconds. Genius!