In a statement on the firm's website, the mobile VoIP outfit says: "Mobile operators 3 and T-Mobile have barred their customers from calling Mobiboo 07911 phone numbers. The companies say this is because of the high charges that BT is making to them to reach Mobiboo, although we believe that this is part of the ongoing anti-VoIP campaign."
While anti-VoIP may not be the right term, it's well known that telcos are doing this. Should they be allowed to do this? Do they have to allow any traffic over their networks? Likely, with most issues surrounding this, it'll end up in the courts.