Quick setup summary (What is an APN? Access Point Names Explained)
This detailed What is an APN? — Access Point Names Explained (UK Guide) guide covers the latest settings, troubleshooting methods, and fixes for common mobile network problems.
You'll need to enter or update APN settings in any of these situations:
After getting a new phone (especially unlocked or refurbished): Unlocked phones that weren't sold by your carrier may not have your carrier's APN pre-configured. This is particularly common with phones bought directly from manufacturers like Google (Pixel) or OnePlus, or devices bought second-hand.
After a factory reset: Resetting your phone to factory settings wipes your APN configuration. If your carrier doesn't push automatic settings when you reinsert the SIM, you'll need to re-enter them.
After switching carriers (keeping your number): When you port your number to a new carrier, you get a new SIM. Some phones hold onto the old APN and don't update automatically. Manually entering the new carrier's APN is often necessary.
After inserting a SIM into an older phone: Phones from 2015 or earlier sometimes don't receive OTA (over-the-air) APN configuration. Manual entry is often required for these devices.
When MMS stops working after a software update: Major Android or iOS updates occasionally reset APN settings, particularly the MMS-specific fields.
Troubleshooting checklist
Starts fast, ends thorough — that's the order here
Recommended setup checks (What is an APN? Access Point Names Explained)
Check the APN via Mobile Network or Cellular Data settings, save it, restart, and confirm data, MMS and hotspot work where applicable.