Dial an exten 157, record the message, hang up, then create call files to dial out to overhead page unit and announce message.

exten => 157,1,Goto(overhead-pager,s,1)

[overhead-pager]
;------record the over head page file-----------------------------------------
exten => s,1,Answer()
exten => s,n,Wait(2)
exten => s,n,Record(pager/currentpage.ulaw,5,60,)    ;mkdir /var/lib/asterisk/sounds/pager
exten => s,n,Wait(2)
exten => s,n,Hangup

exten => t,1,Hangup()

exten => h,1,Goto(page-app,ohp,1)

[page-app]
;------over head page (ohp) call file setup------------------------------------
exten => ohp,1,Set(spooldir=/var/spool/asterisk)
exten => ohp,n,System(echo "Channel: SIP/102" > ${spooldir}/page.call)    ;set the proper sip device to call
exten => ohp,n,System(echo "MaxRetries: 0" >> ${spooldir}/page.call)
exten => ohp,n,System(echo "RetryTime: 60" >> ${spooldir}/page.call)
exten => ohp,n,System(echo "WaitTime: 45" >> ${spooldir}/page.call)
exten => ohp,n,System(echo "Context: page-app" >> ${spooldir}/page.call)
exten => ohp,n,System(echo "Extension: page" >> ${spooldir}/page.call)
exten => ohp,n,System(echo "Priority: 1" >> ${spooldir}/page.call)
exten => ohp,n,System(mv ${spooldir}/page.call ${spooldir}/outgoing/)

;This is where the .call file starts from
exten => page,1,Answer
exten => page,n,NoOp( Waiting for Answer )
exten => page,n,WaitForSilence(1000)
exten => page,n,NoOp(The Page Was Answered)
exten => page,n,Wait(1)
exten => page,n,Playback(pager/currentpage)
exten => page,n,Wait(1)
exten => page,n,System(rm /var/lib/asterisk/sounds/pager/currentpage.ulaw)
exten => page,n,Hangup()

exten => h,1,Hangup()