Depreciation is calculated to write off the cost of items of property, plant and equipment, less their estimated residual value, if any, using
the straight-line method over their estimated useful lives as follows:
Buildings 8 – 30 years
Telecommunications transceivers, switching centers,
transmission and other network equipment
5 – 10 years
Office equipment, furniture, fixtures and others 3 – 10 years
Both the useful life of an asset and its residual value, if any, are reviewed annually.