user A can not call the internal subscriber, after dial the number, he will hear "Sorry, your call has been restricted for bandwidth reason, please redial later."
Change the voip settings by command "config modify voipdomain id 0 maxcallnum 100", problem solved.
Trace the logs by ucmaint, and find error as blew:
[ccm.c 68641][dwCCMNo= 12] CCM_CheckVOIPDomainCallCapability
[ccm.c 68655][dwCCMNo= 12] CCM_CheckVOIPDomainCallCapability, caller limited domainid:0
[ccm.c 23963][Release Line= 40797][dwCCMNo= 12] CCM_ReleaseCallByCaller( ucCause =  )
Check the settings by "show subscribe dn A", find that the user is in VOIP domain test;
Issue command "show voip domain" to check the settings of VOIP domain. We found the maxcallnum of VOIP domain 0 was configured as "0".
Be carefully of seetings in PBX. Log trace is a good way to solve the service problem