To smoke-roast on a charcoal grill: Light the coals (preferably in a chimney starter), then rake the embers into two mounds at opposite sides of the grill with a disposable drip pan positioned in the center. Come time to cook the bird, simply place it on the grate in the center, over the drip pan, and toss a handful of soaked hickory or other wood chips on each mound of coals. (Soaking makes the chips smolder, not catch fire, releasing fragrant clouds of flavorful wood smoke.)
Note: If you want to preserve the drippings for gravy, put the turkey in a sturdy shallow roasting pan and place the pan in the center of the grill grate. When replenishing the coals, protect the bird with another foil drip pan (held vertically, like a shield) or heavy-duty foil so the flying embers and ash don’t contaminate the drippings.
To smoke-roast on a two-burner gas grill: Light one side on high and roast the turkey on the other. On a three-burner gas grill, light the outside or front and rear burners on medium and cook the turkey over the unlit burner in the center. On a four- or six-burner gas grill, light the outside burners and cook the bird in the center. If your gas grill has a dedicated smoker box, place the wood chips in it. Otherwise, you can wrap the chips in heavy-duty foil and poke holes in the top to make a smoker pouch, then place it under the grate directly over one of the burners. I must warn you that gas grills don’t produce nearly as much smoke as charcoal, so even if you’re a diehard gas griller, you might wish to invest in an inexpensive charcoal kettle grill for smoking.