This is the custom snippet (I added some comments that will help people understand) that he adds to do the actual caller-ID unblocking. It's only 8 lines and you add it to your asterisk extensions.conf file:
[inbound]
;For Asterisk 1.4
;workaround to prevent rtp deadlock
exten => 12089068200,1,Playback(silence/1|noanswer)
;save the callerid to a variable
exten => 12089068200,2,Set(passertedid=${SIP_HEADER(P-Asserted-Identity)})
;save the privacy bit to a variable (if it is set)
exten => 12089068200,3,Set(privheader=${SIP_HEADER(Privacy)})
;check if callerid is private
exten => 12089068200,4,GotoIf($[${LEN(${privheader})} > 1]?8)
;send out regular callerids without modification
exten => 12089068200,5,Set(CALLERID(all)=${CUT(passertedid,@,1):5})
exten => 12089068200,6,Dial(SIP/18053414555@flowroute)
;prepend 900 to blocked callerids before unmasking
exten => 12089068200,8,Set(CALLERID(all)=+900${CUT(passertedid,@,1):5})
exten => 12089068200,9,Dial(SIP/18053414555@flowroute)
You gotta change the "18053414555" to your whatever phone number you want to forward calls to is. Also change "12089068200" to whatever number you purchased from flowroute.
i hope that helps and i'll be back soon with more