How to Improve SMS Deliverability when Using Long Numbers in the US

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Overview

Wireless carriers, including AT&T, Verizon, T-Mobile, and Sprint, monitor SMS sent over their networks to prevent the delivery of spam. When messages are sent from a 10-digit long number, carriers will sometimes filter out texts that their systems have flagged. One way to improve deliverability is by using several sending numbers to avoid having all the volume and traffic come through one number. This article will share how many long numbers you should have and how to add them.

As of February 19, 2021, free toll-free numbers will be provided instead of a free long number when someone sets up SMS for the first time. This article is geared toward those who were provided with a free long number.

Recommended Number of Long Codes

Since wireless carriers have stricter SMS filtering policies for long numbers when they are used for application-to-person texting, it's important to limit how many subscribers you send a message to from any one long number. A message sent from a single long number to too many people will likely not be delivered due to filtering. However, SMS messages are priced based on how many you send, not those that are delivered. 

Thus, the number of long numbers an account should have is based on how many SMS subscribers you have. A best practice is to have one long code per every 200 SMS subscribers that you send to regularly.

SMS Subscriber Volume Recommended Number of Long Codes
<200 1
201–400 2
401–600 3
601–800 4
801–1,000 5
1001–1200 6
1,201–1,400
1,401–1,600 8
1,601–1,800 9
1,801–2,000 10

What to Do after Reaching 200 SMS Subscribers

When you have over 200 SMS subscribers, switch to a toll-free number. This provides better deliverability than long codes. Toll-free numbers can also be verified, which makes them even better for your deliverability. 

Another option is to add more long numbers, but this is not recommended. Long numbers only work in the US, have worse deliverability, and (in the long run) are more expensive than toll-free numbers. 

Additional Resources

Check out these articles to learn more about SMS deliverability:

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