T-Mobile takes $100 off the price of iPhone 7 256 GB, offers free iPhone SE (in certain conditions)3
For a limited time, T-Mobile lets you buy an iPhone 7 256 GB for the price of a 128 GB model. More exactly, instead of paying $849.99 for the iPhone 7 256 GB, you'll only pay $749.99 (or $125.99 upfront, and $26.00 per month for 24 months) - this means you'll be saving $100. Unfortunately, the offer only includes the 4.7-inch iPhone 7, so it excludes the larger iPhone 7 Plus.
The second deal that you can currently get at T-Mobile is a BOGO (buy one, get one free) offer. If you purchase any new iPhone model, you can get an additional iPhone SE for free. However, the first iPhone must be purchased in a T-Mobile retail location on EIP (Equipment Installment Plan), and you have to add a new line for the iPhone SE. It looks like you also have to actually pay for the iPhone SE first, and you'll receive a $400 mail-in rebate afterwards. Terms and conditions for this offer are a bit vague, but you'll certainly find more details in T-Mobile stores.
sources: T-Mobile, Twitter