Justice Department said that without the sale of some assets the tie-up "would have substantially lessened competition to the detriment of consumers of mobile wireless telecommunications services in those areas, and likely would result in higher prices, lower quality and reduced network investments."

The deal potentially gives Verizon Wireless, the second-biggest mobile phone company in the United States with 67 million customers, control over the fifth-largest, Alltel, with 13 million.

The transaction also is subject to review by the Federal Communications Commission.

The divestitures required cover the entire states of North Dakota and South Dakota; large portions of the states of Colorado, Georgia, Kansas, Montana, South Carolina, Utah and Wyoming; and portions of the states of Alabama, Arizona, California, Idaho, Illinois, Iowa, Minnesota, Nebraska, Nevada, New Mexico, North Carolina, Ohio and Virginia.

said by EPS :

An interesting thing, the merger has apparently caused the FCC to take a second look at foreign ownership in telecom companies- apparently T-Mobile could be in trouble. (I can't link to the article because it's the Wall Street Journal and you can only get articles for free there if you go via Google News, but type in something like 'T-Mobile foreign ownership' into Google and you should find it)