You can switch between different types of mobile plans, like talk and text plans or data plans. Here's what you need to know:

• You can only make one plan change at a time. If you need to change your start date, you'll have to do a separate request.
• You can start your new plan right away or wait until your next billing cycle.
• You don't need money in your account to change plans, but you won't be able to use your service if your account is unpaid.
• Your plan change will be recorded in your account automatically.
• If you switch to a plan that doesn't work with your data storage, you'll see warnings about losing that saved data.
  
  

For detail step by step click here: https://www.t-mobile.com/support/devices/sim-esim

Yes, devices must be unlocked by the original carrier or OEM and be compatible with the network for them to be used on T-Mobile's network. Some T-Mobile services may not be available or may require additional set up to function properly.
More info here: https://prepaid.t-mobile.com/bring-your-own-device

T-Mobile Prepaid customers get some of the Scam Shield Un-carrier benefits with Scam ID and Scam Block services and free incoming Caller ID.
Scam ID identifies bad actors and shows as Scam Likely on devices, but it doesn't show blocked or unknown caller details.
All calls from identified scammers (such as Scam Likely numbers) are blocked in the network and disconnected before your phone rings when Scam Block is enabled.

You're able to utilize hotspot functionality included in our data plans at no extra cost! Any data used while hotspotting will be deducted from your overall data bucket. If you exceed your data limit, your data speeds will be reduced to 2G speeds. To access more data, you can upgrade your plan by contacting 611 or visiting a T-Mobile store.

The $15 North America Stateside International add-on lets customers on our network unlimited calls from the US, Mexico, or Canada to landlines in 70+ countries and destinations, and mobile lines in 30+ countries and destinations. Plus, get unlimited texting from our network to 215+ countries and destinations, and discounted calling to the rest of the world.

With the $5 Mexico & Canada Unlimited Calling & Texting you get unlimited calling to and from the U.S., Mexico and Canada while on our network or roaming with a partner. Plus get unlimited texting to 215+ countries and destinations, and up to 5GB of high-speed data (or a maximum of your plan’s high-speed data allotment, whichever comes first) while in a coverage area in Mexico or Canada.

Use the country look-up on T-Mobile.com [link: https://www.t-mobile.com/coverage/international-calling] to confirm the per-minute charge for the country you want to call and to see if it is one of the 215+ countries and destinations that can receive unlimited texts as a part of an international add-on.

All international service charges for calls to pay-per-minute countries will be deducted from your available account balance. You will need to have funds in your account in order to complete pay-per-minute calls.

Caller ID is a free tool at T-Mobile that displays a caller’s name and number—even if they're not in your contact list.

All T-Mobile prepaid customers with a capable device on voice plans are eligible for free Caller ID.

It’s easy! Just visit a Retail store or simply dial #436# from your T-Mobile phone, and we’ll hook you up with free Caller ID. To check whether Caller ID is on or off, dial #432#.

Caller ID is available to T-Mobile prepaid voice customers at no extra charge.

• Scam ID warns you when a call is suspected to be an illegal scam call by replacing the Caller ID display with the words “Scam Likely”. Plus, because T-Mobile is able to look beyond the incoming number and tracks actual call behavior, Scam ID can catch spoofed calls as well.
• If you don’t want to see any “Scam Likely” calls, you can activate Scam Block for free by simply dialing #662# on your T-Mobile phone.

Scam ID is free and automatic for all T-Mobile prepaid customers on a capable device; no action required.

To turn on Scam Block, dial #662# from your T-Mobile phone. To turn it off, dial #632#. To check whether Scam Block is on or off, dial #787#.