Lots more XMPP users than signal users 🙂

I've never had a problem with telephathy (either on n900 or using Empathy), but usually I suggest people use Gajim or Psi. But Kopete should still work (even if abandoned) as does Pidgin (even if it is a lowest-common-denominator client).

http://security.stackexchange.com/questions/49782/is-telegram-secure

Kontalk of you like phone numbers, Conversations if you like usernames

Why? This I still the best option. On mobile use Conversations