5. FIXED ASSETS

As of December 31, 2011 and 2012, property, plant and equipment consist of the following (in thousands):

		2011			2012

Telecommunications equipment and towers	5 - 15	$	666,969		$	697,340
Office and computer equipment	3 - 10		47,063			53,579
Buildings	15 - 39		18,017			29,619
Transportation vehicles	3 - 10		7,679			8,610
Leasehold improvements	Shorter of useful life or lease term		20,515			19,876
Land	—		6,653			6,836
Furniture and fixtures	5 - 10		8,120			11,090

Total plant in service			775,016			826,950
Construction in progress			38,375			42,394

Total property, plant, and equipment			813,391			869,344
Less: Accumulated depreciation			(330,188	)		(418,797	)

Net fixed assets		$	483,203		$	450,547

Depreciation and amortization of fixed assets using the straight-line method over the assets' estimated useful life for the years ended December 31, 2010, 2011 and 2012 was $68.5 million, $93.6 million and $96.5 million, respectively.

For the years ended December 31, 2010, 2011 and 2012, amounts of capital expenditures were offset by grants of $1.6 million, $11.8 million and $30.6 million, respectively.

During the year ended December 31, 2012, the Company sold certain network assets used in its wholesale U.S. Wireless business. The Company recorded a gain on this transaction, calculated as follows:

			(in thousands)

Sales proceeds			$	15,629
Less net book value of assets sold:
Property, plant and equipment, cost	12,279
Accumulated depreciation	(8,263	)

Property, plant and equipment, net book value				4,016
Other				8

Total net book value of assets sold				4,024

Gain on disposition of long-lived assets				11,605