BOSH support would be killer for Telepathy on mobile devices (such as the N900) where the user is often only able to access the "Internet" through an HTTP proxy. Using BOSH would enabled such users to tunnel their XMPP connection through said HTTP proxy and thus still use their IM on the go.
Link to XEP, for developpers:
- XEP-0206: XMPP Over BOSH: http://xmpp.org/extensions/xep-0206.html
- XEP-0124: Bidirectional-streams Over Synchronous HTTP (BOSH): http://xmpp.org/extensions/xep-0124.html