I think it makes sense in it's own weird way -- if the broadcaster had said "Call us on ...." it wouldn't have mattered because we don't know the service provid

I think it makes sense in it's own weird way -- if the broadcaster had said "Call us on ...." it wouldn't have mattered because we don't know the service provider behind the phone number. But when they say "follow us on twitter" or "follow us on facebook" they are indirectly endorsing a particular service provider over other similar kinds of service providers.