i'm having the same issue here
on both side (calling and receiving call) no sound at all or some part of it trough my SIP Trunk provider.
internal call are ok
here is the log of a call that had no sound (from 3cx extension to external phone number)
19:50:43.745|.\CallCtrl.cpp(346)|Log2||CallCtrl:

nIncomingCall:[CM503001]: Call(3): Incoming call from Ext.10 to <sip

externalphonenumberhidden)@172.16.0.2:5060><br>
19:50:43.745|.\Extension.cpp(1407)|Log3||Extension:

rintEndpointInfo:[CM505001]: Ext.10: Device info: Device Not Identified: User Agent not matched; Capabilities:[reinvite, replaces, able-no-sdp, recvonly] UserAgent: [3CXPhone 6.0.20943.0] PBX contact: [sip:
[email protected]:5060]<br>
19:50:43.745|.\CallCtrl.cpp(529)|Log3||CallCtrl:

nSelectRouteReq:[CM503010]: Making route(s) to <sip

externalphonenumberhidden)@172.16.0.2:5060><br>
19:50:43.745|.\CallCtrl.cpp(708)|Log2||CallCtrl:

nSelectRouteReq:[CM503004]: Call(3): Route 1: VoIPline

externalphonenumber)@(Ln.10002@(siplinename))@[Dev:sip

my3cxphonenumber)@sip05.unlimitel.ca:5060]<br>
19:50:47.245|.\SLServer.cpp(805)|Error1|MediaServer|MediaServerReporting::STUN:[MS101005] STUN request failed for ports 9004,9005 on STUN server 'stun01.sipphone.com:3478'<br>
19:50:47.245|.\SLServer.cpp(805)|Error1|MediaServer|MediaServerReporting::STUN:[MS201000] Use STUN server 'stun.callwithus.com:3478'<br>
19:50:47.307|.\Target.cpp(441)|Log2||Target::makeOneInvite:[CM503025]: Call(3): Calling VoIPline

externalphonenumberhidden)@(Ln.10002@(siplinename))@[Dev:sip

my3cxphonenumber)@sip05.unlimitel.ca:5060]<br>
19:50:55.995|.\CallLeg.cpp(315)|Log3||CallLeg:

nAnswer:[CM503002]: Call(3): Alerting sip

my3cxphonenumber)@sip05.unlimitel.ca:5060<br>
19:50:55.995|.\Line.cpp(1455)|Log2||Line:

rintEndpointInfo:[CM505003]: Provider:[(my3cxphonenumber)] Device info: Device Not Identified: User Agent not matched; Capabilities:[reinvite, replaces, able-no-sdp, recvonly] UserAgent: [] PBX contact: [sip

my3cxphonenumber)@(mypublicipaddresS):5060]<br>
19:50:58.401|.\CallCtrl.cpp(885)|Log2||CallCtrl:

nLegConnected:[CM503007]: Call(3): Device joined: sip:
[email protected]:62442;rinstance=427cb3a0d73cdb92<br>
19:50:58.401|.\CallCtrl.cpp(885)|Log2||CallCtrl:

nLegConnected:[CM503007]: Call(3): Device joined: sip

my3cxphonenumber)@sip05.unlimitel.ca:5060<br>
19:50:58.557|.\Call.cpp(42)|Log3||??:Currently active calls - 1: [3]<br>
19:51:00.963|.\SLServer.cpp(823)|Critical0|MediaServer|MediaServerReporting::RTPSender:[MS004000] C:3.1: (ACTIVE): Can't send RTP stream to 172.16.0.4:40024 destination unreachable<br>
19:51:00.963|.\SLServer.cpp(823)|Critical0|MediaServer|MediaServerReporting::RTPSender:[MS004000] C:3.2: (ACTIVE): Can't send RTP stream to 209.217.98.154:14618 destination unreachable<br>
19:51:00.979|.\SLServer.cpp(823)|Error1|MediaServer|MediaServerReporting::RTPSender:[MS104000] C:3.1: (ACTIVE) RTP stream to 172.16.0.4:40024 restored.<br>
19:51:00.979|.\SLServer.cpp(823)|Error1|MediaServer|MediaServerReporting::RTPSender:[MS104000] C:3.2: (ACTIVE) RTP stream to 209.217.98.154:14618 restored.<br>
19:51:03.463|.\SLServer.cpp(823)|Critical0|MediaServer|MediaServerReporting::RTPSender:[MS004000] C:3.1: (ACTIVE): Can't send RTP stream to 172.16.0.4:40024 destination unreachable<br>
19:51:03.463|.\SLServer.cpp(823)|Critical0|MediaServer|MediaServerReporting::RTPSender:[MS004000] C:3.2: (ACTIVE): Can't send RTP stream to 209.217.98.154:14618 destination unreachable<br>
19:51:03.479|.\SLServer.cpp(823)|Error1|MediaServer|MediaServerReporting::RTPSender:[MS104000] C:3.1: (ACTIVE) RTP stream to 172.16.0.4:40024 restored.<br>
19:51:03.479|.\SLServer.cpp(823)|Error1|MediaServer|MediaServerReporting::RTPSender:[MS104000] C:3.2: (ACTIVE) RTP stream to 209.217.98.154:14618 restored.<br>
19:51:06.010|.\SLServer.cpp(823)|Critical0|MediaServer|MediaServerReporting::RTPSender:[MS004000] C:3.1: (ACTIVE): Can't send RTP stream to 172.16.0.4:40024 destination unreachable<br>
19:51:06.010|.\SLServer.cpp(823)|Critical0|MediaServer|MediaServerReporting::RTPSender:[MS004000] C:3.2: (ACTIVE): Can't send RTP stream to 209.217.98.154:14618 destination unreachable<br>
19:51:06.010|.\SLServer.cpp(823)|Error1|MediaServer|MediaServerReporting::RTPSender:[MS104000] C:3.2: (ACTIVE) RTP stream to 209.217.98.154:14618 restored.<br>
19:51:06.026|.\SLServer.cpp(823)|Error1|MediaServer|MediaServerReporting::RTPSender:[MS104000] C:3.1: (ACTIVE) RTP stream to 172.16.0.4:40024 restored.<br>
19:51:08.541|.\SLServer.cpp(823)|Critical0|MediaServer|MediaServerReporting::RTPSender:[MS004000] C:3.1: (ACTIVE): Can't send RTP stream to 172.16.0.4:40024 destination unreachable<br>
19:51:08.541|.\SLServer.cpp(823)|Critical0|MediaServer|MediaServerReporting::RTPSender:[MS004000] C:3.2: (ACTIVE): Can't send RTP stream to 209.217.98.154:14618 destination unreachable<br>
19:51:08.557|.\SLServer.cpp(823)|Error1|MediaServer|MediaServerReporting::RTPSender:[MS104000] C:3.1: (ACTIVE) RTP stream to 172.16.0.4:40024 restored.<br>
19:51:08.557|.\SLServer.cpp(823)|Error1|MediaServer|MediaServerReporting::RTPSender:[MS104000] C:3.2: (ACTIVE) RTP stream to 209.217.98.154:14618 restored.<br>
19:51:08.604|.\Call.cpp(1396)|Log2||Call::Terminate:[CM503008]: Call(3): Call is terminated<br>