Here is what I am seeing in Snooper. Messages from my Lync client to the Yahoo client aren't going anywhere due to the Lync client showing the Yahoo client offline when Yahoo client is logged into the mobile Yahoo client.
Incoming presence (client to FE) subscribe from Lync User to Yahoo user
TL_INFO(TF_PROTOCOL) [0]0788.045C::02/16/2012-21:46:13.356.00313762 (SIPStack,SIPAdminLog::TraceProtocolRecord:SIPAdminLog.cpp(125))$$begin_record
Trace-Correlation-Id: 1685186239
Instance-Id: 00631914
Direction: incoming
Peer: 192.168.1.100:61407
Message-Type: request
Start-Line: SUBSCRIBE sip:sgw107.lcs.msg.sp1.yahoo.com:5061;maddr=sgw107.lcs.msg.sp1.yahoo.com;transport=tls SIP/2.0
From: <sip:lyncuser@domain.com>;tag=563efc3f12;epid=ee9bfa2dda
To: <sip:yahoouser@yahoo.com>;tag=0-13c4-4f3d6e38-12de274-ba8b26a
CSeq: 2 SUBSCRIBE
Call-ID: 815deb60c14445e2bedc362ff32f7bca
Via: SIP/2.0/TLS 192.168.1.100:61407
Max-Forwards: 70
Route: <sip:LYNCFE.domain.com:5061;transport=tls;opaque=state:F:Ci.R314900;lr;ms-route-sig=haaRCUGVd36uJycEQCTw-oNHtRz_4Cs0iexZJohvp4jSvaaCWwXXE6PQAA>
Route: <sip:LYNCEDGE.domain.com:5061;transport=tls;lr>
Route: <sip:lcsap.msg.yahoo.com:5061;transport=tls;lr;ms-key-info=mACAAMBe4M1eNsLZ5uzMAQECAAADZgAAAKQAAD4LgUpt3T7cA1UEXzlZFwNlk02Z8yjtY_iVj0NEIouZxkir2det0J2zmZneThS161NSguTyt3hBAtGzValdHwhtXCqXwmsnXES2YaRJyq9Dc3ZG2Mj0e-fKKyeEuv0xxxC25LJBwUM0QVSxyp2a8OTh8CnaNbQ7f-XVB5-m0UZGkYnrGYgbF1P9fPNo_GYph82Cd-Vv5kA3ghet0JR6pE_NewbrFPdKAPPnT5u7J-MbsyWTDganwnF5uTbQTfqGmIPECT5w6a797ZosPeWsPWVDT9e22IbsRf0LovvSIBwELKOssrhgKmDdSI40z0w7me50Ub7Ic3lr9ctaTAWxRyaI;ms-route-sig=eaMlzzgqDsFbaRrq3VJ5A6UULoNvWO>
Contact: <sip:lyncuser@domain.com;opaque=user:epid:Jr9aBdTg11qQXv9V0fywhgAA;gruu>
User-Agent: UCCAPI/4.0.7577.314 OC/4.0.7577.314 (Microsoft Lync 2010)
Event: presence
Accept: application/msrtc-event-categories+xml, application/xpidf+xml, text/xml+msrtc.pidf, application/pidf+xml, application/rlmi+xml, multipart/related
Supported: com.microsoft.autoextend
Supported: ms-benotify
Proxy-Require: ms-benotify
Supported: ms-piggyback-first-notify
Proxy-Authorization: TLS-DSK qop="auth", realm="SIP Communications Service", opaque="6C977E41", targetname="LYNCFE.domain.com", crand="c2426b3b", cnum="128", response="9bbc0beab8cb1967411c92c1914b2dbc572364f1"
Content-Type: application/msrtc-adrl-categorylist+xml
Content-Length: 462
Message-Body: <batchSub xmlns="
uri="sip:lyncuser@domain.com" name=""><action name="subscribe" id="146897200"><adhocList><resource uri="sip:yahoouser@yahoo.com"/></adhocList><categoryList xmlns="
name="state"/><category name="note"/><category name="services"/><category name="contactCard"/><category name="calendarData"/></categoryList></action></batchSub>
$$end_record
Outgoing (FE to Edge) presence subscribe from Lync user to Yahoo user
TL_INFO(TF_PROTOCOL) [0]0788.0C94::02/16/2012-21:46:13.356.00313ddf (SIPStack,SIPAdminLog::TraceProtocolRecord:SIPAdminLog.cpp(125))$$begin_record
Trace-Correlation-Id: 1685186239
Instance-Id: 00631914
Direction: outgoing
Peer: LYNCEDGE.domain.com:5061
Message-Type: request
Start-Line: SUBSCRIBE sip:sgw107.lcs.msg.sp1.yahoo.com:5061;maddr=sgw107.lcs.msg.sp1.yahoo.com;transport=tls SIP/2.0
From: <sip:lyncuser@domain.com>;tag=563efc3f12;epid=ee9bfa2dda
To: <sip:yahoouser@yahoo.com>;tag=0-13c4-4f3d6e38-12de274-ba8b26a
CSeq: 2 SUBSCRIBE
Call-ID: 815deb60c14445e2bedc362ff32f7bca
Via: SIP/2.0/TLS 192.168.1.41:65439;branch=z9hG4bK98373760.CB6F65D2033C5AD5;branched=FALSE
Max-Forwards: 69
Via: SIP/2.0/TLS 192.168.2.100:61407;ms-received-port=61407;ms-received-cid=314900
Route: <sip:LYNCEDGE.domain.com:5061;transport=tls;lr>
Route: <sip:lcsap.msg.yahoo.com:5061;transport=tls;lr;ms-key-info=mACAAMBe4M1eNsLZ5uzMAQECAAADZgAAAKQAAD4LgUpt3T7cA1UEXzlZFwNlk02Z8yjtY_iVj0NEIouZxkir2det0J2zmZneThS161NSguTyt3hBAtGzValdHwhtXCqXwmsnXES2YaRJyq9Dc3ZG2Mj0e-fKKyeEuv0xxxC25LJBwUM0QVSxyp2a8OTh8CnaNbQ7f-XVB5-m0UZGkYnrGYgbF1P9fPNo_GYph82Cd-Vv5kA3ghet0JR6pE_NewbrFPdKAPPnT5u7J-MbsyWTDganwnF5uTbQTfqGmIPECT5w6a797ZosPeWsPWVDT9e22IbsRf0LovvSIBwELKOssrhgKmDdSI40z0w7me50Ub7Ic3lr9ctaTAWxRyaI;ms-route-sig=eaMlzzgqDsFbaRrq3VJ5A6UULoNvWO>
Contact: <sip:lyncuser@domain.com;opaque=user:epid:Jr9aBdTg11qQXv9V0fywhgAA;gruu>
User-Agent: UCCAPI/4.0.7577.314 OC/4.0.7577.314 (Microsoft Lync 2010)
Event: presence
Accept: application/msrtc-event-categories+xml, application/xpidf+xml, text/xml+msrtc.pidf, application/pidf+xml, application/rlmi+xml, multipart/related
Supported: com.microsoft.autoextend
Supported: ms-piggyback-first-notify
Content-Type: application/msrtc-adrl-categorylist+xml
Content-Length: 462
ms-routing-phase: from-uri-routing-done
Message-Body: <batchSub xmlns="
uri="sip:LyncUser@domain.com" name=""><action name="subscribe" id="146897200"><adhocList><resource uri="sip:YahooUser@yahoo.com"/></adhocList><categoryList xmlns="
name="state"/><category name="note"/><category name="services"/><category name="contactCard"/><category name="calendarData"/></categoryList></action></batchSub>
$$end_record
Outgoing presence request (FE to client) from Yahoo user to Lync user
TL_INFO(TF_PROTOCOL) [0]0788.0C94::02/16/2012-21:46:13.434.00315048 (SIPStack,SIPAdminLog::TraceProtocolRecord:SIPAdminLog.cpp(125))$$begin_record
Trace-Correlation-Id: 1685186239
Instance-Id: 00631916
Direction: outgoing
Peer: 192.168.2.100:61407
Message-Type: request
Start-Line: NOTIFY sip:10.10.2.100:61407;transport=tls;ms-opaque=bb3182442f;ms-received-cid=314900;grid SIP/2.0
From: <sip:yahoouser@yahoo.com>;tag=0-13c4-4f3d6e38-12de274-ba8b26a
To: "Lync User"<sip:lyncuser@domain.com>;tag=563efc3f12;epid=ee9bfa2dda
CSeq: 2 NOTIFY
Call-ID: 815deb60c14445e2bedc362ff32f7bca
Via: SIP/2.0/TLS 192.168.1.41:5061;branch=z9hG4bK6B10C4A0.4A937AEA03403AD5;branched=FALSE;ms-internal-info="crdUXxyEx0zutHiAdu2ITKebAlpPfdCXteVUW49e_mezjqepNKZnzJnAAA"
Authentication-Info: TLS-DSK qop="auth", opaque="6C977E41", srand="809B46B5", snum="208", rspauth="82a59a93e775e4f42a370e65940bba87ac5525e1", targetname="LYNCFE.domain.com", realm="SIP Communications Service", version=4
Max-Forwards: 67
Via: SIP/2.0/TLS 192.168.1.19:50880;branch=z9hG4bKDEAA3A7D.842180346CD17AD9;branched=FALSE;ms-received-port=50880;ms-received-cid=30D700
Via: SIP/2.0/TLS 11.22.33.44:1880;branch=z9hG4bKE0ACB88C.AE380675;branched=FALSE;ms-internal-info="daUM26OTmuJ3FEvaKWFvPnz83gPD8A";received=10.10.1.1;ms-received-port=27100;ms-received-cid=10F0B00
Via: SIP/2.0/TLS 11.22.33.44:5061;branch=z9hG4bK-4f3d7929-158a0e5-5aeb436;received=11.22.33.44;ms-received-port=33018;ms-received-cid=b95c300
Subscription-State: active
Event: presence
Contact: <sip:sgw107.lcs.msg.sp1.yahoo.com:5061;maddr=sgw107.lcs.msg.sp1.yahoo.com;transport=tls>
Content-Type: application/pidf+xml
Content-Length: 369
ms-edge-proxy-message-trust: ms-source-type=AuthorizedServer;ms-ep-fqdn=LYNCEDGE.domain.com;ms-source-network=publiccloud;ms-source-verified-user=verified
Message-Body: ----****MESSAGE BODY DELETED****----
$$end_record