According to the report, this is apparently due to the fact that T-Mobile might not have found a way to make its offering different from the competition. T-Mobile’s CEO John Legere had previously indicated that the company’s streaming service would be “disruptive”, but the report from Bloomberg claims that the delay is because the company is still working on it.
The report says that T-Mobile executives were faced with a decision of either launching a “garden-variety streaming platform”, or delaying the service until 2019 where they might have a chance to launch a “groundbreaking product”. Given that there are so many streaming services available right now, launching something considered to be “garden-variety” might not necessarily be the best idea if they’re hoping to compete.
In any case there’s no word on when in 2019 the service might launch, but either way given that we’re approaching the end of the year, it does seem unlikely that it could have launched this year anyway.