If I declare a global variable that must store the DTMF, and I have another incoming call, the same variable is not clear,...

About global variable , we recommend you do NOT use the global variable in multiple lines programming, use the "call session variable" instead. You can use the ITAPICall.User_Data1,User_Data2,User_Data3 propertys to store your own "call session variable". The User_Data Variant, so it can store any kind of data types.