While not common, some phone numbers may have Shortcode texting blocked with their wireless carrier (more often with Sprint/T-Mobile than other carriers). If they do have Shortcode texting blocked, they will not be able to join your List though a Shortcode Keyword or Website Form. If they text your Keyword and receive an auto-response that says "Service access denied", they likely have Shortcodes blocked on their wireless plan. They can either contact their wireless carrier and enable Shortcode texting, or you can add them into your account through an Import, You could also have them text in your Longcode.

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