Talk.to is a popular chat service that is available on iOS, Android, Windows Phone and desktop. Up to now it supports their own TT chat API and also services like Facebook Chat, Google Talk and Window Live.
However in a recent update to their Windows Phone version of the app I noticed that you can no longer add any 3rd party accounts. ITB reached out to Talk.to who emailed us directly and let us know that they will stop supporting all but their own API.
You can read more about this on their blog, but the switch off will happen officially 15th August.
It is a sign of the times unfortunately where big companies like Facebook, Google and Microsoft only want you to use the official apps so they may many API changes each year causing 3rd party apps to break.