It's a little unclear to me what exactly is represented by a gviSmsResponse with responseType == 'reply'.  Is this sent to us when someone replies to an sms that we've sent?  If so, what are the criteria for determining that it was a reply (is there a certain amount of time it looks for between the last sms we sent and an incoming sms).  Maybe if you could just expand a bit in the comments section how grapevine distinguishes between a gviSms and a gviSmsResponse with responseType == 'reply'.