1Scoop ice cream into an 8x4-inch loaf pan; pack ice cream along one long side to fill half of the pan. Cover and freeze until firm, at least 1 hour.
2Meanwhile, bring sugar and 1-1/4 cups water to a boil in a small pot, stirring to dissolve sugar.
3Remove from heat, then add tea bags and grapefruit zest and let steep for 10 minutes.
4Remove and discard tea bags.
5Stir in grapefruit juice. Cover and chill grapefruit mixture until cold, about 1 hour.
6Process grapefruit mixture in an ice cream maker according to manufacturer's instructions. Pour sorbet into the empty side of the pan alongside the ice cream. Cover and freeze until firm, about 2 hours.
7To serve, spoon across ice cream and sorbet to form swirled scoops.