Gracias Lembas for the information, Jabber Open Source License, Version 1.0 (#josl)
The license is a free software license, incompatible with the GPL. It permits relicensing under a certain class of licenses, those which include all the requirements of the Jabber license. The GPL is not a member of that class, so the Jabber license does not permit relicensing under the GPL. Therefore, it is not compatible.
