I used to use beltclips, but inevitably the clip would fail or the phone would brush up against something, resulting in the phone hitting the ground (or in one particularly spectacular incident, falling into a puddle on rain-soaked pavement) with pieces going in all directions. (I have several Motorola V180 phones that I broke that way that I scavenge parts from to keep my wife's phone working.)

Now, I tend to carry my phone in a front pocket (either pants or shirt), and wear a Plantronics bluetooth earpiece. If you carry a briefcase (or messenger bag or whatever), put the phone in that instead.