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T-Mobile Add a Line: A Complete Guide

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Adding a line to take advantage of multi-line cell phone plan discounts or the latest T-Mobile add a line promotion can be a great way to save money on your monthly phone bill. Whether you’re adding a significant other, a child, or just going in with friends on a group plan, the process for adding a line on T-Mobile is simple, especially with this step-by-step guide.

Want to find the best phone deals available now at T-Mobile and other top wireless carriers when you add a line? Try our free, unbiased Phone Deal Finder below:

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How to Add a Line on T-Mobile

You’ve already checked off the two most challenging parts of adding a new line to your account: identifying who you want to share the benefits with and finding a wireless carrier you like. Now let’s look at four steps for how to add a line on T-Mobile:

Step 1: Prepare Necessary Information

Before reaching out to a T-Mobile customer service representative, be sure to have all the necessary information on hand. That includes your account number, the personal details of the person you’d like to add, and your plan’s current details. If you’re adding a new person to your account, you’ll need their full name, date of birth, and social security number. To add a device, you’ll need the make, model, and IMEI number.

Step 2: Choose a Plan

Do your research before reaching out to customer service. With T-Mobile, you and your plan-mates can’t mix and match cell phone plans—you must all be on the same plan, so it’s important to know what to look for in a wireless plan and really understand everyone's mobile data needs.

For help finding the best T-Mobile cell phone plan to meet your needs, try our Plan Finder and check out our easy-to-understand T-Mobile unlimited plan guides: T-Mobile Essentials Saver | T-Mobile Essentials | T-Mobile Go5G | T-Mobile Go5G Plus | T-Mobile Go5G Next  

Step 3: Contact Customer Service

When it comes to contacting customer service, there are several ways to request to add a line, including the following:

  • By phone: The quickest way to receive direct assistance is by calling T-Mobile’s customer service line.
  • Chat: If you prefer typing over talking, the chat feature on or T-Mobile apps is a convenient way to contact customer service.
  • In-store: For those who prefer speaking to someone in person, visit a local T-Mobile store.

Step 4: Confirm and Activate

After finalizing your plan selection, review and confirm everything with the customer service representative. Once confirmed, they’ll begin activating your new line. Activation may differ depending on whether you’re activating a new device or adding a new user to your plan. For reference, we recommend reading our quick hot-to on activating your T-Mobile SIM card.

T-Mobile Add a Line Promotions

Whether you’re switching to T-Mobile or adding a new line to your existing T-Mobile account, T-Mobile is known for offering great phone deals for new customers and upgraders. The best T-Mobile phone offers are usually reserved for flagship devices like the iPhone 15, Galaxy S24, and Pixel 8 series. For easy access to a list of T-Mobile’s latest switch / add-a-line promotions, check out (and bookmark!) our up-to-date lists of T-Mobile phone deals and T-Mobile iPhone deals

Note that there are often restrictions on T-Mobile cell phone promos (especially those “iPhone on Us” deals). Eligibility requirements may include a qualifying trade-in device and/or a premium T-Mobile unlimited plan

One big plus with any T-Mobile add-a-line promotion (and all T-Mobile offers) is that the promotional credit is paid out over 24 months instead of 36 months, which is the norm among other wireless carriers. 

Why Add a Line?

The most common reason for adding a line to your T-Mobile phone plan is to add a family member, like when your child gets their first phone. You can also combine phone plans with friends or roommates to take advantage of multi-line discounts. As you add more lines to your plan, the cost of each line decreases. Adding people and lines to your mobile phone plan can be a great way to lower an everyday expense for those closest to you as well as for yourself.

But a reduced phone bill isn’t the only reason to add someone to your plan. For people sharing household expenses, you can consolidate phone bills on a single plan to have fewer bills and plans to manage. 

Cost savings, extra perks, and family-centric features are all good reasons to add someone to your mobile phone plan. Just be sure that whoever you add is someone you trust since, as the plan owner, you will be financially responsible for the entire plan cost, including the cost of any new phones you or your plan-mates acquire. Think of it the same way as taking on a roommate in an apartment for which you hold the lease.

How Much to Add a Line to T-Mobile

Wondering how much it costs to add a line to your T-Mobile phone plan? It all comes down to what plan you’re on. The best plan depends on how much data you need, how frequently you use your phone as a hotspot, and whether you value perks like streaming services and early phone upgrades.

For example, at this writing, one phone line on the T-Mobile Essentials Saver, the entry-level T-Mobile unlimited plan, costs $50, but it drops to $40 per line for two lines and $33 per line for three lines. You get the idea. While less expensive, this plan doesn’t have as many bells and whistles as other T-Mobile plans.

If, on the other hand, you go with the mid-level T-Mobile Go5G plan because you need more premium data, hotspot data, and streaming perks, the cost will be $75 per month for one line but drops to $130 per month for two lines, with additional discounts for up to five lines.

The Bottom Line

By adding a friend or family member to your T-Mobile cell phone plan, you can take advantage of multi-line discounts and phone offers.

T-Mobile makes it easy to add a line, and Navi makes it easy to sort through the best phone deals for switchers and upgraders with our free unbiased Phone Deal Finder. Sharing has never been easier.

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