T-Mobile news for Wednesday about the wireless company joining the S&P 500 has TMUS stock up.

T-Mobile (NASDAQ:TMUS) is joining the S&P 500 thanks to a couple of different changes. The first change is that the index has relaxed some of its rules, which allows TMUS to join it.

The rule change is that companies no longer have to have 50% of their shares in the hands of public investors. That is good t-Mobile news as only has 37% of its outstanding shares belonging to public investors, reports Barron’s.

The other reason that T-Mobile is able to join the S&P 500 is that a new spot has opened up on the index. This spot was previously held by Red Hat. However, that company is no longer on the public market after being acquired by IBM (NYSE:IBM).

The T-Mobile news about is joining the S&P 500 is actually a little ahead of its debut on the index. TMUS won’t be officially replacing Red Hat on the index until next week, Yahoo Finance notes.

While T-Mobile is joining the S&P 500, there’s no guarantee it will be a part of the index for long. This is due to the company currently attempting a merger with rival wireless company Sprint (NYSE:S).

Following the T-Mobile news about the company joining the S&P 500, TMUS stock was up 4% as of Wednesday afternoon. The stock is also up 15% since the start of the year.

As of this writing, William White did not hold a position in any of the aforementioned securities.