US SIM Shows Signal but No Data? APN Setup and Troubleshooting Guide

2026-10-19

The short answer: an APN (Access Point Name) is the gateway address your phone uses to reach the carrier's data network — one wrong character can leave you with full signal bars and no internet. iPhones usually configure it automatically when you insert the SIM; Android phones, especially models bought outside the US (Xiaomi, Huawei, Oppo, Vivo), often need it set by hand. Get it right and data plus MMS come alive.

1. When you need to set the APN manually

• Your Android shows signal bars but no data — the classic case.
• Calls work, but mobile data or picture messages don't.
• No data right after swapping SIMs or switching between dual SIMs.
• Your eSIM activated successfully but the data connection keeps spinning.
• iPhones rarely need manual APN entry, though a major iOS update can occasionally wipe the profile.

2. How to add an APN on Android (menu names vary by brand)

• Open Settings → Connections (or Mobile network) → Access Point Names (APN).
• Tap + or Add to create a new APN.
• Enter the values from the table in section 3 for your carrier — fill only the listed fields and leave everything else at its default.
• Open the menu (three dots) → Save, then back in the APN list, tap to select the one you just created so its radio button is filled.
• Toggle Airplane Mode on and off, or restart the phone, so it re-registers on the network.

3. Carrier APN values (verified against the carriers' official support pages)

• T-Mobile (and lines on its network): APN fast.t-mobile.com — all lowercase, don't drop the hyphen between "t" and "mobile"; MMSC http://mms.msg.eng.t-mobile.com/mms/wapenc; MCC 310 / MNC 260; APN type default,supl,mms (commas with no spaces); protocol IPv4/IPv6.
• Lycamobile USA: APN data.lycamobile.com; MMSC http://lyca.mmsmvno.com/mms/wapenc; username lmus / password plus. If your card shipped with different values, use those.
• AT&T: APN phone; MMSC http://mmsc.mobile.att.net; MMS proxy proxy.mobile.att.net, port 80; MCC 310 / MNC 410.
• Fill only the fields listed above; leave the rest blank or at their defaults — don't improvise.

4. Still offline? Run through this checklist

• Confirm it's selected: the new APN must actually be selected in the list — an unselected APN does nothing.
• Restart: reboot the phone or toggle Airplane Mode so it re-registers on the network.
• Check the plan: make sure the plan is active and data isn't used up — your seller can check the status.
• Check the lock status: the phone must be carrier-unlocked; a locked phone gets no signal on another carrier's SIM.
• Try 4G first: in network mode, switch to 4G/LTE and test, then switch back to 5G auto once data works.
• On iPhone: go to Settings → General → Transfer or Reset iPhone → Reset → Reset Network Settings (this wipes saved Wi-Fi passwords); or open Settings → General → About and accept any carrier-settings update prompt.
• Still stuck? Screenshot your APN screen and send it to the seller — one look is usually enough to spot the problem.