In reading this thread, a few things come to mind:
Please be careful in using any tweaks or changes made for the i900. The i910 (American VZW version) Is just different enough that nothing is a given, so please do a backup before attempting anything. I have seen a lot of bricking due to flashing i900 ROMs and some tweaks not working out as described!!
If iContact doesn't work as you intend, another cool one is PocketCM:
http://pocketcm.com/contact.php
It works great on the Omnia and it includes a threaded SMS part that I like MUCH better than the WM version, it is free (or you can donate) and is always being tweaked + supported!
The lock tweak while in a call does work, but it disables certain icons on the dialer screen (along the right side if I remember correctly) so it wasn't worth it to me!
Adrynalyne is covering your questions pretty well, but in case either one of you want to do more reading/finding about tweaks, I started a thread where I am trying to get them all in one place, and there are a lot of them listed along with resources, and hopefully a lot more to come!! (please let me know if you know of any not listed so I can add them to the top)
http://forum.ppcgeeks.com/showthread.php?t=51532