Can TI chip CC2540 be used for mobile phone access with bluetooth?
The CC2540 from TI is a System-on-Chip with a Bluetooth Low Energy radio. Bluetooth Low Energy is a low-power variant of Bluetooth that was introduced in the latest Bluetooth v4.0 specification.

Bluetooth low energy (somtimes shortened BLE) uses 1 Mbps GFSK modulation format and a frequency-hopping spread spectrum in the 2.4 GHz frequency band. BLE allows longer sleep (inactive) times for a battery-powered device, and the protocol has less connection overhead for setting up/closing a connection, so it is more power effective. However, it is not intended for transferring huge amounts of data, so for that you will still want to use "classic" Bluetooth with higher data rates.

The CC2540 can communicate with your mobile phone (via the radio) only if your mobile phone supports Bluetooth low energy. At the moment, I think it is only the Apple iPhone 4GS and the Motorola RAZR that contains Bluetooth chipsets that has Bluetooth low energy enabled.

It is expected that all Bluetooth chipsets used in upcoming mobile phones, tablets and laptops will have support for both classic Bluetooth and Bluetooth low energy (i.e. it will be a so-called "dual-mode" Bluetooth chip). Most Bluetooth chipsets in mobile phones today can become a dual-mode chipset only by updating its firmware, but this isn't done retroactively on old phones, only on new phones.