Making unwanted calls is the single biggest concern I had about finally getting a smartphone. So, I've eventually found this combination ensures these kinds of calls don't happen:
- I've used LudusP to remap my "Green" and "Phone" keys to something innoculous ("Owner" and "Calc", respectively)
- I use "Butler" to enable the two-key keyguard
- I use "TakePhone" as the primary dialer, and have disabled almost all one-tap dialing options, plus I have it set to automatically enable keyguard after finishing a call. (I think that last point is relevant, 'cause an incoming call disables keyguard, so it's possible (guessing) that might be how youse guys' keyguard was turned off, then you made an automatic redial by pressure holding down the green key (IIRC))
Not only does this mean that not anyone could just pick up and use my phone, but I've yet to make an unwanted or accidental call this way.