Something

#extensions.conf

exten => s,1,Answer()
exten => s,n,Swift("press a key")
exten => s,n,Read(KEYS)
exten => s,n,Set(PRESSED=${SWIFT_DTMF}${KEYS})
exten => s,n,Verbose(${PRESSED})

#swift.conf
[general]
goto_exten=yes