We are using SPA400, Asterisk Server and SPA8000. We found the problem of SPA400 about calling in and calling out related with mobile system AIS provider (GSM 1800) in Thailand. The problem is the sound is down, so we have solved this problem by turning up the volume (adjusted db in SPA400). As a result, there is the acho sound between conversation. If we turn down db in SPA400 under 8 db, our customers' side hear our sound a little bit. Please kindly send us the way to solve the problem soon. Thank you in advance.