Next, open FMP, go to Scrips -> ScripMaker and click New for a new script. Double-click the "Perform AppleScript" command in the left window. Double-click the "Perform AppleScript command" in the top right window, and when the window opens, make sure Native AppleScript is selected and paste in the following:
-- change what's in the quotes below
property thePrefix: "YOUR PREFIX"
property thePhoneFieldName: "YOUR PHONE FIELD NAME"
initModem "/dev/cu.modem" with "~^M~AT&F1E0S7=45S0=0L2^M"
tell application "FileMaker Pro"
activate
set theNumber to thePrefix &
(cell thePhoneFieldName of current record)
ignoring application responses
dial modem "ATDT"&theNumber
end ignoring
display dialog thenumber & return & ¬
"Dialing in Progress: Disconnect?" ¬
buttons {"Disconnect"} default button 1 giving up after 10
hang up
end tell
Close everything up and run the script.

