Inspired by this post, installing this CAB will rid you of the auto-keypad lock when you start a call. This is for English language devices only.
Feedback please... i'm considering a simple toggle app too (like my OmniaSIP and OmniaTHREAD apps).
Technical info - this is the SECDialer.dll from the DXHI2 ROM, patched to not write the lock entry to registry, not to display the big graphic and re-signed to give it a valid signature.
MoDaCo.OmniaPatchedDialler.CAB 216.25KB 4121 downloads
MoDaCo.OmniaPatchedDiallerDutch.CAB 216.29KB 573 downloads