Comcast CMCSA 0.58 % is tiptoeing into the wireless business to defend its broadband franchise. It may ultimately decide to jump in with both feet, with big implications for T-Mobile US. TMUS -3.11 %  The cable giant plans to launch a wireless service by mid-2017, using a combination of Wi-Fi and airwaves leased from Verizon Communications, VZ 0.14 % Chief Executive Brian Roberts said at an investor conference Tuesday. The service, which will be marketed to existing customers as part of a bundle of services, could help Comcast retain customers. It could also set the stage for a deal with a carrier like T-Mobile as the need to own a wireless broadband offering becomes clearer.  For Comcast, which said nearly a year ago that it would begin testing a wireless service, the move suggests it believes a wireless presence is necessary. As network technology improves and amid increasing mobile video consumption, wireless internet traffic should continue to rise—even if the speed and quality of the connection don’t quite match that of fixed-line broadband. Comcast needs to offer wireless to capture that growth, and bundling it with video services makes sense.  Now the question is whether leasing Verizon’s network will make sense over the long haul. The terms of the deal between the two companies aren’t public and Comcast has said it doesn’t need to own its own network. But some analysts say the history of such deals suggests it won’t reap the benefits of wireless without owner’s economics.  Enter T-Mobile: Once a takeover target for Sprint, S -6.62 % the company has embarked on an aggressive strategy over the past few years to add subscribers and become more profitable. It said Tuesday that it has added 753,000 new postpaid subscribers so far in the third quarter, pushing it ahead of some analysts’ estimates for the quarter as a whole. Despite these additions and strong iPhone 7 preorders, both of which cut into profitability, the company maintained its 2016 outlook for earnings before interest, taxes, depreciation and amortization. Owning T-Mobile would let Comcast benefit from this momentum and give it instant access to a nationwide wireless network.  Granted, Comcast may be bidding against T-Mobile in the government’s continuing auction for broadcast airwaves. But any spectrum it buys there will be of little use without a network. Comcast may also face competition from other potential bidders for T-Mobile, including Cablevision owner Altice ATC 3.69 % or Charter Communications CHTR 0.62 % if those companies hold similar views on the value of a wireless presence.  The auction rules prevent bidders from having strategic discussions, so deal-making speculation will heat up when it ends. That could be as soon as the end of this year.  Comcast’s wireless appetite makes T-Mobile look even tastier.
Comcast’s new wireless service may prompt it to consider buying its own network one day and T-Mobile US looks like an obvious choice.