Unlike the standard canvas-and-velcro variety, the Mint Mobile wallet is a place to digitally store credit for your Mint Mobile service, and it can be used a couple different ways:
Purchase Extra 4G LTE
If you run out of data before your data reset date, you can purchase more 4G LTE data using credit in your Mint Mobile Wallet.
Use your Mint Mobile wallet to make international calls at low per-minute rates.
You can add money to your Mint Mobile wallet by logging into your account at my.mintmobile.com and selecting Load Wallet. Here, you can add $5, $10 or $20 to your wallet. This balance does not expire.