The KDE Telepathy contact list already supports contact groups, but these seem to be derived straight from the contact properties stored in the remote systems. This means that e.g. Facebook and Skype contacts are always grouped into a single group and cannot be moved to other groups. This feature should probably be implemented as part of the metacontact support. Possibly so that the visible group is based on the metacontact and the network specific contact group info is just ignored.
Confirmed, plan is to make this part of the metacontacts solution storing the tags there.
Dear user, unfortunately Telepathy is no longer maintained. Please migrate to another solution, e.g. for Jabber a possibility is Kaidan, for Matrix a candidate is NeoChat.