What “Unknown Subscriber” Means

It means the SIM card or phone number isn’t recognized at all by the mobile network’s database — usually the HLR (Home Location Register).

The message comes from the carrier’s core network and indicates:

• Your SIM’s IMSI (subscriber ID) is not registered in the network database.

• The SIM may be deactivated, corrupted, or not provisioned for service.

• Sometimes it appears when the network is migrating or updating records, or if the SIM is too old and no longer supported (e.g., 2G-only SIMs on a 4G/5G network).

Step-by-Step Troubleshooting

1. Restart & Reinsert SIM

• Power off your phone.

• Remove the SIM card, wait 30 seconds, reinsert it carefully, and power back on.

• Check if it connects to the network (signal bars + carrier name).

2. Try SIM in Another Device

• If the same “Unknown Subscriber” appears → the SIM is likely faulty or deactivated.

• If it works in another phone → your current device may have network or SIM slot issues.

3. Check for SIM or Account Deactivation

• If your number was inactive for a long time (no calls, SMS, or top-ups for 90+ days), the carrier may have recycled or deactivated it.

• Contact your carrier’s support and ask them to check if the IMSI or MSISDN is active in their system.

4. Replace or Re-provision the SIM

If the SIM is:

• Physically damaged, too old, or not LTE-capable,
  → you’ll need a replacement SIM (same number) from your carrier.

• Provisioning error on the carrier side,
  → ask them to refresh the HLR/VLR registration or re-provision your line.

Optional Checks You Can Do

• Network mode: Ensure your phone supports the network bands (e.g., LTE/3G).

• No signal at all: Could be local tower issues — try the SIM in another area.

• Dual SIM phones: Try swapping slots; sometimes the inactive SIM slot causes the message.

When to Contact the Carrier

If it still says “Unknown Subscriber” after trying the above:

• Contact your mobile network’s customer service directly.
  Tell them:

  “I’m getting an ‘Unknown Subscriber’ error when trying to connect or send SMS. Please check if my IMSI is active and provisioned for voice/SMS/data.”

They can instantly see in their system whether your number exists or if it needs reactivation or replacement.