NEW YORK/FRANKFURT, June 4 (Reuters) – Sprint Corp has agreed to pay about $40 per share to buy T-Mobile US Inc , a person familiar with the matter said, marking further progress in the attempt to merge the third and fourth-biggest U.S. mobile network operators. The $40 price represents a 17 percent premium to T-Mobile US’s closing share price on Wednesday, giving it a valuation of more than $32 billion and the shares have more than doubled in price since the group bought smaller rival MetroPCS a year ago.