1. Preheat a grill to medium-high heat. Combine the butter, cumin, cayenne and 1/2 teaspoon salt in a small bowl. Brush half of the butter mixture over the ears of corn and wrap each ear in a piece of heavy-duty foil.
2. Place the wrapped ears of corn on the grill and cook, turning every 10 minutes, until the corn feels soft on all sides when you squeeze it with tongs, about 30 minutes. Remove from the grill and cool for about 5 minutes.
3. Unwrap the corn, being careful of steam, and place on a serving platter. Brush with the remaining butter mixture, sprinkle with the cilantro and serve with lime wedges.