Property, Plant and Equipment
Property, plant and equipment (PP&E), including improvements that extend useful lives, are recognized at cost. Depreciation on property, plant and equipment is generally calculated using the straight-line method based on estimated economic useful lives of 3 to 30 years for buildings and improvements and network equipment, site costs and related software and 3 to 12 years for non-network internal use software, office equipment and other. Leasehold improvements are depreciated over the shorter of the lease term or the estimated useful life of the respective assets. We calculate depreciation on certain network assets using the group life method. Accordingly, ordinary asset retirements and disposals on those assets are charged against accumulated depreciation with no gain or loss recognized. Gains or losses associated with all other asset retirements or disposals are recognized in the consolidated statements of comprehensive loss. Depreciation rates for assets are revised periodically to account for changes, if any, related to management's strategic objectives, technological changes or obsolescence. Repair and maintenance costs and research and development costs are expensed as incurred.
We capitalize costs for network and non-network software developed or obtained for internal use during the application development stage. These costs are included in PP&E and, when the software is placed in service, are depreciated over estimated useful lives of 3 to 5 years. Costs incurred during the preliminary project and post-implementation stage, as well as maintenance and training costs, are expensed as incurred.
