Blocking Outgoing Calls

Does anyone have much experience of blocking specific outgoing calls by area code? I've been through the FAQ's & help but it doesn't seem to come up much except for blocking all international calls.

What I specifically want to do is to allow calls to US & Canadian area codes & to the countries covered by the international free calls add on & exclude everything else, so for instance I would want to allow calls to UK land lines - numbers starting +441 or +442 but exclude those costly international cell phone calls (numbers starting +447).

The system seems pretty functional & well documented for blocking incoming numbers, area codes etc so am wondering if anyone out there can give me an idea of how easy, difficult or possible even it is to block specific outbound calls.

I suspect, given the number of areas & countries I would want to block a list of allowed outbound call areas would make more sense / less work / less monitoring for changes than a list of blocked areas.

To complete the picture, my objective is to keep costs to within the annual fee by avoiding any additional call charges & still letting other occupants of our house use the phone without having to rely too heavily on a trust based system. I would also want to avoid the phone being able to access premium rate / toll charge numbers in the US - while this phone is for our house in the US I'm actually from the UK so am a bit unfamiliar with those sort of services here - in the UK premium rate numbers (numbers that can charge in excess of US$50/min to call) are fairly common but I don't know if those sort of numbers can be accessed from the US & if they can how I would go about blocking them as well)

All replies much appreciated - Tech support at VOIPo have said its all possible but I haven't yet got anything that goes into the mechanics of setting the system up for this so I don't know how to do it & most importantly how easy it is to set up & maintain.

Thanks in advance, Mat.