Hi Pascal,
Have a look at the release notes below, it lloks like the 7925 will not be supported until the next devpack for 4.2(3) which is 4.2(3.55);
Table 1: Cisco Unified Communications Manager Release Requirements for Cisco Unified Wireless IP Phone 7925G Support
CUCM Release
Minimum Service Release (SR) Required
DevicePack Required?
DevicePack Minimum Release
Notes
4.1(1) - 4.1(3)
-
Yes
4.1(82)
Install device pack
4.2(1) - 4.2(3)
-
Yes
4.2(3.55)
Install device pack
4.3(2)
-
Yes
4.3(2.08)
Install device pack
5.1(1) - 5.1(2)
5.1(3)
Yes
5.1.3.4114-2
Upgrade to 5.1(3) and install device pack
5.1(3)
-
Yes
5.1.3.4114-2
Install device pack
6.0(1)
-
Yes
***DevicePack Minimum Release 6.0.1.3112-1
Install device pack
6.1(1)
6.1(2)
Yes
6.1.2.1120-1
Upgrade to 6.1(2) and install device pack
6.1(2)
-
Yes
6.1.2.1120-1
Install device pack
7.0(1)
-
Yes
7.0.1.12004-1
Install device pack
http://www.cisco.com/web/software/282074289/23369/cmterm-7925-sccp.1-3-1-Readme.html
Hope this helps! You may be able to get this from TAC :)
Rob