SIPp

SIPp is a free Open Source test tool / traffic generator for the SIP protocol.
http://sipp.sourceforge.net/

Run:
sipp -sn type -d duration(sec) -s test number SIP Server -l calls -i Local IP
sipp -sn uac -d 30000 -s 500 192.168.10.229 -l 5 -i 192.168.10.5