The main source of revenue of the Company includes various telecommunications services in different streams. The information of disaggregation of revenue please refer to Note 44.

The information of performance obligations in customer contracts, please refer to Note 3 Summary of Significant Accounting Policies for details.

	Domestic Fixed Communi- cations Business		Mobile Communi- cations Business		Internet Business		International Fixed Communi- cations Business		Others		Total
	NT$		NT$		NT$		NT$		NT$		NT$
	(In Millions)
Main Products and Service Revenues
Mobile services revenue	$	—	$	63,906	$	—	$	—	$	—	$	63,906
Sales of products		1,731		35,702		4		251		3,601		41,289
Local telephone and domestic long distance telephone services revenue		29,996		—		—		—		—		29,996
Broadband access and domestic leased line services revenue		22,453		—		—		—		—		22,453
Data Communications internet services revenue		—		—		21,137		—		—		21,137
International network and leased telephone services revenue		—		—		—		8,724		—		8,724
Others		11,923		1,269		8,509		4,449		806		26,956
	$	66,103	$	100,877	$	29,650	$	13,424	$	4,407	$	214,461

	December 31
	2018
	NT$
	(In Millions)
Trade notes and accounts receivable (Note 11)	$	30,076
Contract assets
Products and service bundling	$	7,123
Other		109
Less : Loss allowance		(19	)
	$	7,213
Current	$	4,869
Noncurrent		2,344
	$	7,213
Contract liabilities
Telecommunications business	$	8,193
Project business		4,508
Products and service bundling		106
Other		476
	$	13,283
Current	$	10,688
Noncurrent		2,595
	$	13,283

The changes in the contract asset and the contract liability balances primarily result from the timing difference between the satisfaction of performance obligations and the payments collected from customers. Significant changes of contract assets and liabilities recognized resulting from product and service bundling were as follows:

	Year Ended December 31
	2018
	NT$
	(In Millions)
Contract assets
Net increase of customer contracts	$	4,126
Reclassified to trade receivables		(7,532	)
	$	(3,406	)
Contract liabilities
Net increase of customer contracts	$	16
Recognized as revenues		(194	)
	$	(178	)

The Company applies the simplified approach to providing for expected credit losses prescribed by IFRS 9, which permits the use of lifetime expected loss provision for receivables. Contract assets will be reclassified to trade receivables when the corresponding invoice is billed to the client. Contract assets have substantially the same risk characteristics as the trade receivables of the same types of contracts. Therefore, the Company concluded that the expected loss rates for trade receivables can be applied to the contract assets.

Revenue recognized for the period that was included in the contract liability at the beginning of the period was as follows:

The Company considered the past experience and the default clauses in the telecommunications service contract and believes the commissions and equipment subsidy paid for obtaining contracts are expected to be recoverable; therefore, incremental costs of obtaining contracts are recognized as an asset. Amortization expense of incremental costs of obtaining contracts for the year ended December 31, 2018 was $1,941 million.

As of December 31, 2018, the aggregate amount of transaction price allocated to performance obligations for non-cancellable telecommunications service contracts that are unsatisfied is $38,909 million. The Company expects to recognize revenue when service is provided over contract terms in the next 36 months, $24,388 million, $11,581 million and $2,940 million for 2019, 2020 and 2021, respectively. The variable consideration collected from customers on nonrecurring basis resulting from exceeded usage from monthly fee and revenue recognized for contracts that the Company has a right to consideration from customers in the amount corresponding directly with the value to the customers of the Company’s performance completed to date have been excluded from the disclosure of remaining performance obligations.

As of December 31, 2018, the aggregate amount of transaction price allocated to performance obligations for non-cancellable project business contracts that are unsatisfied is $20,990 million. The Company recognizes revenues when the project business contract is completed and accepted by customers. The Company expects to recognize such revenue of $3,656 million, $12,893 million and $4,441 million in 2019, 2020 and 2021, respectively. Project business contracts whose expected duration are less than a year have been excluded from the aforementioned disclosure.