Many users have told me their 3G/4G LTE data network connection is broke after installing a custom ROM. Well, in most of these cases, it can easily be fixed by manually setting the APN (Access Point Name). This applies to any GSM networks such as AT&T or T-Mobile. For CDMA networks like Sprint or Verizon, they also use APNs but you don’t have to set them and should work out of the box.
Couple weeks ago when I was planning my trip to Thailand, I searched all over the internet and wondered if I was going to be able to get 3G data working (since Thailand doesn’t have 4G LTE yet) while I stayed for couple weeks.