Your telephony provider will be able to provide you with a rate sheet that outlines the different charges for different numbers. This is as far as I know the only definative way of working out the charge, pretty much everything else is just assumption & guideline - as a for instance, 0800 numbers are free on my mobile contract, but on most of the big name mobile companies they are premium numbers and even outside your bundle.
As far as cloaking of numbers - if I understand your concern, you get charged for the number you dial - if the recipent then diverts it to a premium number - for whatever reason - they pay the premium fee. My company does this, we provide a free fax number, but we divert it to a premium rate 'fax to e-mail' service. We pay the premium as our fee for using the service, our clients pay nothing since they called a free phone number.
Hope that helps