LG G2 — Echo problem for the person who I am talking with while making voip call

Hi,
I am using LG G2 (D802 32 gb 4G) made in Korea and whenever i talk to people using different VoIP software, they complain about echo .. (they are listening their sound). When i called from these same software from my friends' phone there is no problem at all.. So, its only with my mobile. When i use ear phone its fine, no echo.. only it comes when i use without ear phone. And also i found two VoIP software without this issue . those works perfectly. but most VoIP have this issue, which works perfectly on other phones.. Problem exists even after I upgraded and downgraded OS. So, please someone tell me that why this problem and how to solve it ..... Thanks in advance...