Yes, MicroB supports tel: and sip: URLs, but there's a problem with the version that shipped with PR 1.2. See https://bugs.maemo.org/show_bug.cgi?id=10404 . FIx is in comment #6, namely add these two keys, boolean, set to false, to your about:config: network.protocol-handler.warn-external.sip network.protocol-handler.warn-external.tel