"TONS of stuff goes on in offices that has no place in the work place - gossip, eating (and not just at lunch time; in all offices I've worked in there is eating pretty much all day long), mumsnetting, non-work phone calls, office romances (that is fecking annoying actually), facebook etc. etc."
While holding religious views and not being discriminated against for holding them is perfectly clear, in a work environment, there are clear issues concerning demonstrating beliefs (eg wearing a crucifix, etc).
As for using faclilities for non-work activities, whether making personal calls (or on behalf of some group/organisation), or using the internet, it just needs a company policy document to lay down what is acceptable and what is not, in work time or using work equipment.
If it is clear that all phone calls made to/from office phone lines are recorded, and all use of internet not for work related to the company/organisation is banned, then it makes it clear to individuals to spend time in coffee/tea breaks or at lunch time to (a) leave the building, or (b) use their own mobile phone (or laptop) for private calls (or Skype) or internet access... definitely no "jokes" using company e-mail! That's already been a sacking offence if it tarnishes the company/organisation name.
general "isuse" becomes a clear abuse, and after verbal or written warnings could be a cause for dismissal. I feel sure most places have a more relaxed attitude than mine, but only for what constitutes 'reasonable' use, and if someone didn't put in sufficient hours on getting work done, or was running up a big phone bill, it would be spotted and dealt with.