I believe you should add one, not subtract. E. g. if TTL on the phone is set to 64, you'll want router to send packets with TTL 65, so that one extra hop (from

I believe you should add one, not subtract. E. g. if TTL on the phone is set to 64, you'll want router to send packets with TTL 65, so that one extra hop (from router to phone) brings it down to 64 and the carrier can't tell the difference.