Below is information on a new default setting that T-Mobile implemented:

T-Mobile's message blocking
​T-Mobile has a feature that allows recipients on their network to enable a setting which blocks ANY SMS sent to their mobile number from business-type sender numbers, such as Short Codes, Toll-Free, and 10DLC-Routed Long Codes. This includes OTP codes, appointment notifications, etc. from any SMS sender network.
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SMS sent to T-Mobile recipients with this feature enabled often returns error 30005 in the SMS logs, indicating the block. This can only be removed by having the recipient contact T-Mobile Support directly to request that setting be turned off. Specifically, the mobile user must call 611 directly from their T-Mobile device experiencing the issue – or if using another device, call 1-800-937-8997 – and request "Toll- Free and Shortcode Blocklist" setting to be removed from their account.

As a result of the above, only T-Mobile customers with this setting enabled won't be able to receive SMS until they turn off the setting, which in our experience is a very small subset of users - for these T-Mobile customers, they will be impacted when waiting at other businesses beyond yours as well, regardless of whether those businesses are using NextMe or other waitlist platforms / SMS providers.

We assure you that our SMS messaging reliably delivers for all other carriers.

T-Mobile may change the default setting at some point after experiencing a high volume of customer complaints, but it may help to add info on your signage letting your guests with T-Mobile know something along the lines of: There is a known recent T-Mobile default setting that is blocking some T-Mobile users from receiving business SMS text messages, call 1-800-937-8997 – and request "Toll- Free and Shortcode Blocklist" setting to be removed from your account.