Twilio error 30006 means you are attempting to send an SMS to a number that belongs to a landline, a VoIP line that does not support SMS, or a carrier that is simply not reachable from Twilio's network. This is a permanent failure for that specific number in its current state, unlike 30003, which is temporary. Every message sent to a landline will fail with this code, and retrying without removing the number from your list will waste your message budget and degrade your sender reputation.
What Causes This Error
The most direct cause is sending SMS to a number that is classified as a landline in carrier databases, such as a traditional copper phone line or a PBX extension that cannot receive SMS. VoIP numbers provisioned without SMS capability, which includes many business phone systems and older VoIP providers, also return 30006 because they have no SMS path registered with the carrier. Numbers assigned to paging services, fax machines, or machine-to-machine SIMs fall into this category as well. Geographic routing gaps are a less common cause: some international carriers, especially in developing markets, do not have bidirectional SMS routing agreements with Twilio, making their number ranges unreachable.
How to Fix It Step by Step
Query the Twilio Lookup API for every number returning 30006 by calling GET lookup.twilio.com/v1/PhoneNumbers/{number}?Type=line_type_intelligence and examining the line_type field in the response. Numbers with a line_type of landline, voip, non-fixed-voip, or null should be moved to a suppression list and excluded from future SMS sends. For international numbers where the Lookup API returns an unreachable carrier result, cross-reference with Twilio's supported countries list in the Console under Messaging, then Geographic Permissions to determine if SMS delivery to that country is available on your account. Update your contact database to flag these numbers as non-SMS-capable and route any future communication attempts to a voice call or email channel instead.
How to Prevent It from Recurring
Integrate a line type check at the point of phone number collection using the Twilio Lookup API with line_type_intelligence, so landline and VoIP numbers are flagged before they ever enter your SMS contact list. Build a pre-send filter in your messaging pipeline that queries the line_type field for any number that has not been validated within the last 30 days, since numbers can change type when ported or when a subscriber upgrades their service. For international campaigns, verify carrier coverage by checking Twilio's country-specific pricing pages and SMS coverage matrix before scheduling sends to new geographic markets. Periodically re-validate your entire contact list using Lookup in batch mode, as business numbers especially can switch from mobile to VoIP over time as companies change their phone infrastructure.
When to Call a Specialist
If a significant percentage of your contact list is returning 30006 and you have already filtered landlines through the Lookup API, you may have a list acquisition problem where the source of your contacts is supplying non-mobile numbers without proper labeling. A specialist can help you design a data acquisition audit to trace where invalid numbers are entering your system and implement controls to stop them at the source. For international routing gaps where specific country ranges are unreachable, a specialist can advise on alternative routes, local carrier direct connections, or MVNO bypass options that may restore reachability. A 30006 rate above 5 percent in any campaign is a data quality red flag that always deserves investigation before money continues to be spent on failed sends.
Conclusion
Error 30006 is a firm signal to remove the number from your SMS list permanently and switch to another contact channel. If this error is blocking your production system, contact our team and we will diagnose and fix it within the hour.
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