Twilio Programmable Wireless SIM cards provide connectivity to T-Mobile's cellular network in the United States, to T-Mobile's GSM carrier roaming partners in the US, and to T-Mobile's roaming partners outside the US.

Notice: T-Mobile USA, Twilio’s connectivity partner for Programmable Wireless in the United States and one the networks available on Super SIM, is phasing out its 2G and 3G networks. We recommend users move to LTE devices for new and existing SIMs. For full details, see Alert: Programmable Wireless T-Mobile 2G and 3G Shutdown (Twilio Docs).

If you are in an area with ample signal strength but cannot connect to the cellular network, try the following:

1. Verify the device operates on the required frequency bands.
2. Verify the APN is set on the device to wireless.twilio.com
3. Make sure the rate plan associated with this SIM offers the desired capability; e.g. ensure a SIM you are trying to send messages to is using a rate plan with messaging enabled, and make sure a SIM outside the United States is on a rate plan that enables international roaming. 
4. Has the SIM data usage cap for the month been reached? If so, assign the SIM to a different rate plan, and the SIM will be able to reconnect
5. Is the issue persistent, or intermittent?
   • If persistent:
     • It could be a location-specific issue, try in a different location.
     • It could be a hardware-specific issue, try in a different device. We recommend dropping the SIM in an iPhone or flagship Android device as these are high-quality hardware that support a large number of network bands. 
   • If intermittent:
     • Try power cycling the device
     • Try performing a SIM network reset. 
     • If the device is stationary while losing connection it could be due to poor local network conditions.

A word about cellular network unpredictability

Cellular networks are uniquely impacted by environmental factors like buildings, local geography, and weather; for example, it's possible to be in a highly-populated area and still not be able to attach to the network due to interference from buildings, or network capacity limitations.

Network tuning and turn-downs, like the retirement of 3G 1900 MHz spectrum in North America, can result in a location having coverage one day, and then no coverage the next. Tuning of cell towers to optimize network resources, changes in third-party coverage reseller licensing agreements, and roaming partner changes can also result in inconsistent coverage at certain locations.

Transient network issues and outages are also unfortunately unavoidable. Twilio has no visibility into carrier network conditions at any given time.