Кодек в SJPhone судя по всему стоит SJ Labs GSM 6.10 CODEC.
Перевел по вашему совету на SIP. Теперь с PBX звонки проходят на SJPhone нормально и даже поговорить можно

Вот только звук идет с существенной заедржкой где-то в полсекунды. Как то лечится?
А вот звонок с SJPhone на PBX так и не удается сделать. Вот лог SJPhone:
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2009-09-28 12:47:37.634 UDP LOCAL->192.168.3.50:5060
INVITE sip:102@192.168.3.50 SIP/2.0
Via: SIP/2.0/UDP 192.168.3.51;branch=z9hG4bKc0a80333000000584ac0b06900001c790000001f;rport
From: "unknown" <sip:192.168.3.51>;tag=58cc1c9890
To: <sip:102@192.168.3.50>
Contact: <sip:192.168.3.51>
Call-ID: 6F46F8D5B31346FCB3C6AB978AAABB5A0xc0a80333
CSeq: 1 INVITE
Max-Forwards: 70
User-Agent: SJphone/1.65.377a (SJ Labs)
Content-Length: 365
Content-Type: application/sdp
Supported: replaces,norefersub,timer
v=0
o=- 3463130857 3463130857 IN IP4 192.168.3.51
s=SJphone
c=IN IP4 192.168.3.51
t=0 0
m=audio 49170 RTP/AVP 3 97 98 8 0 101
c=IN IP4 192.168.3.51
a=rtpmap:3 GSM/8000
a=rtpmap:97 iLBC/8000
a=rtpmap:98 iLBC/8000
a=fmtp:98 mode=20
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=setup:active
a=sendrecv
19:47:37 SIP.Network DEBUG
2009-09-28 12:47:37.865 UDP 192.168.3.50:5060->LOCAL
SIP/2.0 100 Trying
Via: SIP/2.0/UDP 192.168.3.51;branch=z9hG4bKc0a80333000000584ac0b06900001c790000001f;rport
From: "unknown" <sip:192.168.3.51>;tag=58cc1c9890
To: <sip:102@192.168.3.50>
Call-ID: 6F46F8D5B31346FCB3C6AB978AAABB5A0xc0a80333
CSeq: 1 INVITE
User-Agent: AddPac SIP Gateway
Content-Length: 0
19:47:37 SIP.Network DEBUG
2009-09-28 12:47:37.865 UDP 192.168.3.50:5060->LOCAL
SIP/2.0 404 Not Found
Via: SIP/2.0/UDP 192.168.3.51;branch=z9hG4bKc0a80333000000584ac0b06900001c790000001f;rport
From: "unknown" <sip:192.168.3.51>;tag=58cc1c9890
To: <sip:102@192.168.3.50>;tag=bf60e113a4
Call-ID: 6F46F8D5B31346FCB3C6AB978AAABB5A0xc0a80333
CSeq: 1 INVITE
User-Agent: AddPac SIP Gateway
Content-Length: 0
19:47:37 SIP.Network DEBUG
2009-09-28 12:47:37.875 UDP LOCAL->192.168.3.50:5060
ACK sip:102@192.168.3.50 SIP/2.0
Via: SIP/2.0/UDP 192.168.3.51;branch=z9hG4bKc0a80333000000584ac0b06900001c790000001f;rport
From: "unknown" <sip:192.168.3.51>;tag=58cc1c9890
To: <sip:102@192.168.3.50>;tag=bf60e113a4
Call-ID: 6F46F8D5B31346FCB3C6AB978AAABB5A0xc0a80333
CSeq: 1 ACK
Max-Forwards: 70
User-Agent: SJphone/1.65.377a (SJ Labs)
Content-Length: 0
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То есть такое ощущение, что ap200 дает отлуп SJPhone. Почему?