(Telecompaper) AT&T has announced it is offering T-Mobile customers USD 450 per line when they switch to AT&T and trade in an eligible smartphone. Beginning 3 January, under the limited-time offer, T-Mobile customers who switch to AT&T can trade-in their current smartphone for a promotion card of up to USD 250, which can be used toward AT&T products and services. Trade-in values vary based on make, model and age of the smartphone. T-Mobile customers can receive an additional USD 200 credit per line when they transfer their mobile service to AT&T and choose an AT&T Next plan and buy a device at full retail price or activate a device they currently own. T-Mobile said in a response that the AT&T offer must be the result of a "terrible" Q4 and holiday season. "I'm flattered that we have made them so uncomfortable," said T-Mobile CEO John Legere in a statement. He noted the company used the money received from AT&T after its failed takeover of T-Mobile to help develop its "superior" network and new offers. "Consumers won't be fooled...nothing has changed; customers will still feel the same old pain that AT&T is famous for," he said, adding that the operator will unveil new offers at CES in the coming week.