I would think it's because that's a number used to offer 'cheap' calls to international destinations, as as such, is a use which is approved of. The amount you are paying for the call pays for the cost of the international leg. Bypassing this is a quick way to drive the company out of business. The example you quote is often used for calls to Ecuador, and is charged at 7p/min. You can get calls for about half this via otherproviders, e.g. various betamax brands offer calls via VOIP for €0.04/min. (See
http://backsla.sh/betamax and choose a brand that best matches your calling patterns.)
We normally only help finding numbers for companies where the only reason for an 08* is to make profit off you rather than give you a service for the money.
Basically, read the stickies about posting requests.