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

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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
1,401–1,600 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, you can either: 

  1. Switch to a toll-free number
  2. Add more long codes to your account

The best practice is migrating to a toll-free number, but we discuss both options below. 

Switching to a Toll-Free Number

We recommend migrating from long codes to a toll-free number, as this provides better deliverability than long codes. You can also get toll-free numbers verified, which makes them even better for your deliverability. Further, switching to a toll-free number is simpler and cheaper in the long run, as you won't need to continue adding long numbers to your account. 

For step-by-step instructions, check out this article on migrating from a long number to a toll-free number

Adding Long Codes to Your Account

If you want to keep only using long numbers, you can do this in Klaviyo. You can add up to 400 long codes to your account in batches of no more than 20 numbers at a time. (If you need more than 400 long numbers, please contact Klaviyo Support and we can add more.) From your dashboard, click your organization name in the upper right-hand corner. Then, click Account > Settings > SMS Settings. The first section in that page is the Sending Numbers section. There, select the Additional Numbers dropdown and click Request Additional Numbers. Note that each new long code you request comes with a subscription fee of $1/month.


After clicking this, a modal will pop up. A best practice is to check the Redistribute new number(s) and existing sending number(s) box. Klaviyo uses “sticky sending,” which means that a recipient will always receive communications from the same phone number. When you add new long codes, checking this box will make sure your phone numbers are evenly distributed among your SMS subscribers. Note that when you redistribute your numbers, some recipients will see a shift in the number from which they receive SMS from your brand.


Note that a subscriber can opt out by texting STOP to any number on your Klaviyo account — even if it's not the number associated with their profile via sticky sending. 

Additional Resources

Check out these articles to learn more about SMS deliverability:

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