I'm have a mix of 7965 and 7945 cisco handsets (see below for details). Even with no headset connected (to the headset port under phone), if the handset is in the cradle with the 'headset' button on the front of the phone selected, the call can still be heard from the earpeace of the handset. I would have though that the 'headset' button should divert all audio away from the handset port but it looks as if the audio is present on both ports.
MAC Address 002290049A9A
Host Name SEP002290049A9A
Phone DN 8822
App Load ID jar45sccp.8-4-1ES10.sbn
Boot Load ID tnp65.8-3-1-21a.bin
Version SCCP45.8-4-1SR2S
Expansion Module 1
Expansion Module 2
Hardware Revision 9.0
Serial Number FCH12299DW1
Model Number CP-7965G
Message Waiting No
UDI phone
Cisco Unified IP Phone 7965G, Global, Gig Ethernet, Color
CP-7965G
V04
FCH12299DW1
Time 13:06:25
Time Zone GMT Standard/Daylight Time
Date 19/02/09
DHCP Server 10.100.129.104
BOOTP Server No
MAC Address 002290049A9A
Host Name SEP002290049A9A
Domain Name uk.vtbcapital.internal
IP Address 10.101.10.218
Subnet Mask 255.255.255.128
TFTP Server 1 10.100.184.11
Default Router 1 10.101.10.129
Default Router 2
Default Router 3
Default Router 4
Default Router 5
DNS Server 1 10.101.129.3
DNS Server 2 10.101.129.4
DNS Server 3
DNS Server 4
DNS Server 5
Operational VLAN Id 442
Admin. VLAN Id
Unified CM 1 10.101.184.11 Active
Unified CM 2 10.100.184.11 Standby
Unified CM 3
Unified CM 4
Unified CM 5
Information URL
Directories URL
Messages URL
Services URL
DHCP Yes
DHCP Address Released No
Alternate TFTP No
Forwarding Delay No
Idle URL
Idle URL Time 0
Proxy Server URL
Authentication URL
SW Port Configuration 100 Full
PC Port Configuration 100 Full
TFTP Server 2 10.101.184.11
User Locale English_United_Kingdom
Network Locale United_Kingdom
Headset Enabled Yes
User Locale Version
Network Locale Version
PC Port Disabled No
Speaker Enabled Yes
GARP Enabled No
Video Capability Enabled No
Voice VLAN Enabled Yes
Auto Line Select Enabled No
DSCP For Call Control CS3
DSCP For Configuration CS3
DSCP For Services Default
Security Mode Non Secure
Web Access Enabled Yes
Span to PC Port No
PC VLAN
CDP: PC Port Yes
CDP: SW Port Yes
LLDP-MED: SW Port Yes
LLDP: PC Port Yes
LLDP Power Priority Unknown