iPhone 6 Plus, been struggling with searching.../ No service for past few weeks.
Tried this method and it works for my iPhone 6 Plus (suggested by "johnidx" on Feb 27, 2017 on iFIX forum)
1. Power off your iPhone ( my is iPhone 6 Plus)
2. Remove sim slot
3. Place the iPhone on a soft padded surface, screen face down, and hit on the back of your iPhone few times
4. Place your SIM card back and power up. And works for me so far
If signal lost again, tried this method once more.
Dropping my iPhone 6 Plus twice with soft shell case might be the root cause.
Unfortunately with today's feather weight smartphone designs, they are so tightly packed inside, dropping your iPhone basically is death sentence for the phone.
Get a tough graded phone case if you want the phone last you long time.