giving a mobile no. out is entirely different. The are putting themselves at risk from unwanted calls but no one will know their name, email address and place of work.
When people open a new online account it requires email address, name and password usually, some require home address which can be found via the Electoral Register for �5..
How do you know one of your mates wouldn't forward this to their mates in the office, then they each forward it to their mates etc..
My sister forwards me these and I never see her it's crazy she does this but I get everyones details she works with and the friends of them too.
I use to work in an office and these things flew around, they obviously began from one person sending it to a few and withing hours it had been opened by thousands if not millions of people.. But it's ok I'm sure your mates will not forward it to anyone..