REGEDIT4

[HKEY_LOCAL_MACHINE\Security\Phone\Skin\Dialer\Portrait\VerbButton]
"bmpNormal"="\\Windows\\ktf_speedup_port.png"
"bmpPressed"="\\Windows\\ktf_speeddown_port.png"

[HKEY_LOCAL_MACHINE\Security\Phone\Skin\Dialer\Landscape\VerbButton]
"bmpNormal"="\\Windows\\ktf_speedup_land.png"
"bmpPressed"="\\Windows\\ktf_speeddown_land.png"