A merger between T-Mobile (TMUS) and Sprint (S) would make for a much stronger number three player in wireless and bring "massive" synergies, but regulatory approval, while not out of the question, remains uncertain, Jefferies analyst Mike McCormack tells investors in a research note.

The analyst's initial pro forma analysis, which assumes an all-stock transaction at current market prices and synergies ramping to a $4.5B run rate in year three, suggests T-Mobile could be worth more than $90 per share in a deal scenario, or 43% above the current price.

The stock closed yesterday down $1.17 to $62.89. McCormack also continues to see "significant value" in T-Mobile on a standalone basis. He has a Buy rating on the shares with an $80 price target.