The Jabber way of handling personal information (name, addresses, phone numbers, etc) is “vCards” encoded in XML. You can get information about a user by running M-x jabber-vcard-get, and you can edit your own information by running M-x jabber-vcard-edit.
The form for editing your information can be slightly confusing — you are allowed to enter any number of addresses, phone numbers and e-mail addresses, each of which has a set of orthogonal properties. You can add and remove items with the [INS] and [DEL] buttons, respectively.
This is also where you set your avatar (see Avatars). The size of your avatar file is limited to 8 kilobytes.