Well.. In Sweden and Norway we often encourage jest, jokularity, and friendly teasing.. It creates a relaxed work-place-attitude, and increase communication between co-workers.. both of which in the end leads to more efficiant workers. The increased efficiancy and productivity that comes from a non-estranged, relaxed (and dare I say happy) staff is also a good reason why it's bad to straight out forbid personal phone-calls or e-mails. I would say professionalism lies not in ignoring the possibility for in-office goofing, but in not letting in-office teasing get in the way of everyone being able to perform their function (Don't goof around customers, supliers, or sub-contractor, make sure that your goofing don't turn in to bullying, takes up too much time, or in any other way get out of hand)
But everything in moderation (including moderation).