The only downside (for many) to using super secure messengers is that they do not require any e-mail address or phone number to register, so the net result often is you have no idea if some of your contacts join later, and they won't see you either.
For XMPP Quicksy allows you to create a separate account on their service with your phone number (if you wish to) and in this way you can be alerted if any contacts join via the Quicksy service. This account is completely separate from your day-to-day XMPP account (or you could use it for day-to-day if you wanted to make your phone number known).
A spin-off of the popular Jabber/XMPP client Conversations with automatic contact discovery. Sign up with your phone number and Quicksy will automatically—based on the phone numbers in your address book—suggest possible contacts to you.