Changes in property and equipment account for the years ended December 31, 2018 and 2017 are as follows:

	Cable and wire facilities			Central office equipment			Cellular facilities			Buildings and improvements			Vehicles, aircraft, furniture and other network equipment			Communications satellite			Information origination and termination equipment			Land and land improvements			Property under construction			Total
	(in million pesos)
As at December 31, 2016
Cost		196,652			115,461			202,581			25,914			55,973			966			14,596			3,440			50,070			665,653
Accumulated depreciation, impairment and amortization		(148,622	)		(96,793	)		(138,189	)		(16,992	)		(48,300	)		(966	)		(12,338	)		(265	)		—			(462,465	)
Net book value		48,030			18,668			64,392			8,922			7,673			—			2,258			3,175			50,070			203,188
Year ended December 31, 2017
Net book value at beginning of the year		48,030			18,668			64,392			8,922			7,673			—			2,258			3,175			50,070			203,188
Additions (Note 4)		3,410			687			6,512			159			2,682			—			1,878			1			24,970			40,299
Disposals/Retirements		(8	)		—			(123	)		(38	)		(316	)		—			—			—			(134	)		(619	)
Reclassifications (Note 13)		5			3			—			3			(7	)		—			—			14			(143	)		(125	)
Impairment losses recognized during the year (Note 5)		—			—			(389	)		—			—			—			—			—			(3,524	)		(3,913	)
Transfers and others		7,612			3,945			8,031			1,285			1,959			—			1,343			3			(24,178	)		—
Translation differences charged directly to cumulative translation adjustments		—			(1	)		—			(1	)		(4	)		—			—			—			—			(6	)
Depreciation of revaluation increment on investment properties transferred to property and equipment charged to other comprehensive income		—			—			—			(2	)		—			—			—			—			—			(2	)
Depreciation and amortization		(11,594	)		(5,340	)		(28,242	)		(1,274	)		(4,106	)		—			(1,357	)		(2	)		—			(51,915	)
Net book value at end of the year		47,455			17,962			50,181			9,054			7,881			—			4,122			3,191			47,061			186,907
As at December 31, 2017
Cost		207,220			119,642			209,504			27,076			58,964			—			17,595			3,458			50,585			694,044
Accumulated depreciation, impairment and amortization		(159,765	)		(101,680	)		(159,323	)		(18,022	)		(51,083	)		—			(13,473	)		(267	)		(3,524	)		(507,137	)
Net book value		47,455			17,962			50,181			9,054			7,881			—			4,122			3,191			47,061			186,907
Year ended December 31, 2018
Net book value at beginning of the year		47,455			17,962			50,181			9,054			7,881			—			4,122			3,191			47,061			186,907
Additions (Note 4)		1,278			565			758			120			1,158			—			2,107			—			52,504			58,490
Disposals/Retirements		(10	)		(27	)		(60	)		(140	)		(95	)		—			—			—			(9	)		(341	)
Reclassifications (Note 13)		19			(1	)		—			127			(23	)		—			—			1,117			—			1,239
Transfers and others		10,409			8,237			37,881			265			1,465			—			1,176			—			(59,433	)		—
Translation differences charged directly to cumulative translation adjustments		—			3			—			1			(3	)		—			—			—			—			1
Deconsolidation of a subsidiary		—			—			(65	)		(794	)		(273	)		—			—			—			—			(1,132	)
Impairment losses recognized during the year (Note 5)		(299	)		(292	)		(858	)		(480	)		(29	)		—			—			—			—			(1,958	)
Depreciation of revaluation increment on investment properties transferred to property and equipment charged to other comprehensive income		—			—			—			(2	)		—			—			—			—			—			(2	)
Depreciation and amortization		(11,381	)		(10,480	)		(17,499	)		(2,162	)		(3,382	)		—			(2,334	)		(2	)		—			(47,240	)
Net book value at end of the year		47,471			15,967			70,338			5,989			6,699			—			5,071			4,306			40,123			195,964
As at December 31, 2018
Cost		217,773			128,321			217,164			26,546			58,711			—			20,823			4,576			40,123			714,037
Accumulated depreciation, impairment and amortization		(170,302	)		(112,354	)		(146,826	)		(20,557	)		(52,012	)		—			(15,752	)		(270	)		—			(518,073	)
Net book value		47,471			15,967			70,338			5,989			6,699			—			5,071			4,306			40,123			195,964

Interest capitalized to property and equipment that qualified as borrowing costs amounted to Php1,524 million, Php816 million and Php566 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 5 – Income and Expenses – Financing Costs. The average interest capitalization rate used was approximately 5% each for the years ended December 31, 2018, 2017 and 2016.

Our net foreign exchange differences, which qualified as borrowing costs, amounted to Php411 million, Php106 million and Php111 million for the years ended December 31, 2018, 2017 and 2016, respectively.

The cost of fully depreciated property and equipment that are still being used in the Group’s operations amounted to Php171,867 million and Php196,612 million as at December 31, 2018 and 2017, respectively.

As at December 31, 2018 and 2017, the estimated useful lives of our property and equipment are estimated as follows:

In December 2017, Smart and DMPI recognized an impairment loss of Php3,913 million pertaining to network improvement project involving spectrum refarm and long-term evolution rollout. These assets include Radio Access Network, or RAN, equipment such as base transceiver sets, base station controllers, access radios, antennas, radio network controllers, power and related support facilities, among others, including software licenses and implementation services affecting the Quezon City and Marikina areas.

In 2018, Digitel and DMPI recognized an impairment loss amounting to Php1,096 million and Php862 million, respectively, as a result of the full migration of fixed line subscribers to PLDT network for Digitel and continued network convergence strategy for DMPI.

See Note 3 – Management’s Use of Accounting Judgments, Estimates and Assumptions – Impairment of non-financial assets.