I doubt this is a Jabber issue, try this thread - https://supportforums.cisco.com/discussion/10912916/limit-maximum-number-calls-ip-phone
Jabber works on windows protocol handler, jabber registers with sip: and tel: protocol handler.
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/jabber/10_6/CJAB_BK_C56DE1AB_00_cisco-jabber-106-deployment-and-installation-guide/CJAB_BK_C56DE1AB_00_cisco-jabber-106-deployment-and-installation-guide_appendix_01111.html