# 10DLC Registration and Why Phone Validation Matters for SMS Compliance > 10DLC registration is required for A2P SMS in the US. Learn how phone validation helps you stay compliant and get the most out of your approved throughput. Published 2025-07-20, updated 2026-10-03 by Marcus Whelan. Canonical: https://checkthatphone.com/blog/10dlc-registration-phone-validation If you send A2P SMS in the US over local numbers, 10DLC registration is mandatory. T-Mobile, AT&T, and Verizon want your brand and your campaigns registered through [The Campaign Registry](https://www.campaignregistry.com/) (TCR) before you send a single automated text. Skip it and your messages get filtered, throttled, or blocked. A campaign can be fully registered and still underperform when its contact list is full of landlines and dead numbers, because every one of those sends fails. What people miss is that registration is the start, not the finish. Phone validation is what keeps the throughput you were approved for from quietly eroding. ## What 10DLC actually is 10DLC stands for 10-digit long code, and it lets businesses send A2P (Application-to-Person) SMS over standard 10-digit phone numbers. Before this system existed, plenty of companies fired automated texts through local numbers with no registration at all. Carriers now actively filter that unregistered traffic. Registration happens in two steps: 1. Brand registration, where your business identity is verified through TCR. 2. Campaign registration, where each use case (marketing, 2FA, alerts, and so on) is registered separately with a description and sample messages. Your approved throughput (messages per second) and your daily message limits depend on your trust score, which comes from brand vetting, plus the campaign type you registered. ## Why phone validation matters for 10DLC Registration decides how much you're allowed to send. Validation decides how much of that actually reaches a phone that can receive a text. ### Protect your sender reputation Your trust score comes from brand vetting at registration, not from delivery rates, so validation won't raise it. What validation protects is how your traffic looks after approval. Sends to invalid, disconnected, or landline numbers fail, and a high failure rate is the clearest sign of a stale or bought list. Validating numbers before you send is the cheapest way to keep those failures out of your traffic. ### Avoid carrier filtering Registration does not exempt you from monitoring. Carriers keep filtering A2P traffic after approval, and the industry rulebook for consent and content is CTIA's [Messaging Principles and Best Practices](https://www.ctia.org/the-wireless-industry/industry-commitments/messaging-principles-and-best-practices). Validation removes sends to numbers that can't receive them before they ever leave your system. ### Make your throughput count Your throughput limit is set by your vetting score and campaign type, and clean data won't change that number. It does decide how much of it you spend on real people: every message sent to a dead number or a landline is capacity and budget you can't use on a reachable one. ### Stay aligned with your registered use case A 10DLC campaign has to match what you registered it as. Send marketing messages under a 2FA registration and you have violated the terms. Validation does not police your content, but line type data does keep you honest about where messages go: SMS to mobile numbers, not landlines. ## What to validate before sending For every number on your messaging list, check: - Line type. Send SMS to mobile numbers, plus any landline confirmed SMS-capable. Most landlines can't receive texts (about 7% of the landlines we check are SMS-capable), and some VoIP numbers silently drop them. [Line type lookup](/line-type-lookup-api) and the [landline SMS check](/landline-sms-lookup) cover both cases. - Deliverability. Confirm the number is active and able to receive messages. - Carrier and porting status. Make sure the message routes to the network the number lives on now, not the one it was issued on. - Deactivation status. Drop anything recently deactivated. CheckThatPhone [returns all of these fields](/docs) in a single API call, so validating a number is one request, not four. For a whole list before a campaign, upload a CSV instead ([bulk phone validation](/bulk-phone-validation)). If you're still working out which of your traffic counts as A2P in the first place, see [A2P vs P2P SMS](/blog/a2p-vs-p2p-sms-messaging), and for what landlines do to a send, see [why your SMS campaign is silently dropping landlines](/blog/why-your-sms-campaign-is-silently-dropping-landlines-and-how-to-detect-text-enabled-ones). ## Where to start Clean data is the part of 10DLC compliance that nobody registers for and everybody pays for. Validate before you send: it protects your trust score, holds your throughput, and keeps you out of the carrier filtering that quietly kills a campaign. [Read the API documentation](/docs) to wire validation into your messaging workflow, or [explore pricing plans](/pricing) to start validating at the volume you actually send. --- CheckThatPhone is a phone validation API for US and Canada numbers: https://checkthatphone.com (docs: https://checkthatphone.com/docs.md, pricing: https://checkthatphone.com/pricing.md).