Надо цифры DMTF поместить в отдельный контекст и добавить m, чтобы набиралась только одна цифра.
[ivr]
exten => 1,1,Verbose(Switch to 102 from ivr)
same => n,Dial(SIP/102,300)
same => n,Hangup()
exten => 1,1,Verbose(Switch to 102 from ivr)
same => n,Dial(SIP/102,300)
same => n,Hangup()
[incoming]
same => s,Answer
same => n,Set(TIMEOUT(response)=15)
same => n,Background(announce/ivr,m,,ivr)
same => n,Background(silence/5,m,,ivr)
same => n,Goto(callcenter,74953223232,1)
same => n,Set(TIMEOUT(response)=15)
same => n,Background(announce/ivr,m,,ivr)
same => n,Background(silence/5,m,,ivr)
same => n,Goto(callcenter,74953223232,1)