Sprint today announced a guaranteed minimum $200 trade-in value for all T-Mobile customers that port over their number and trade in their working T-Mobile smartphone.

The offer stands until April 9 and can be combined with Sprint’s promise of up to $350 per line to cover ETFs and other expenses.

Sprint’s new focused attack on T-Mobile comes after a busy week or so for the Uncarrier. T-Mobile last week announced new lower cost prepaid plans. This week, T-Mobile introduced a $50 unlimited LTE plan through MetroPCS and also announced Smartphone Equality, its plan to ditch credit checks for loyal customers.

In 2014, Sprint says it bought back more than 3 million phones and remanufactured more than 80 percent. The carrier says that to date its phone trade-in programs generated more than $1 billion in savings for the company through reusing certified pre-owned devices.