From a document I found on the web related to !dea
Our ability to provide a quality mobile network is dependent on the Spectrum allocated to us.
Spectrum is defined as the distribution of wavelengths and frequencies that exist in a continuous range and have a common characteristic, containing electromagnetic frequencies used for electronic communications including, amongst other things, mobile communications.
A mobile network’s capacity is, to a certain extent, limited by the amount of frequency Spectrum available for its use. Thus the capacity of our network is limited by the amount of Spectrum allocated to us. The
DoT manages and allocates frequency Spectrum to mobile operators. Spectrum is generally allocated within two frequency bands: 900 MHz and 1800 MHz. The 900 MHz frequency band is preferable as it leads to a lower overall capital cost as compared to the 1800 MHz band. Frequencies in the 900 MHz band generally are granted to the first operators in a particular Circle. We have been allocated the 900 MHz frequency bands for seven of the Circles in which we currently operate, namely Andhra Pradesh, Gujarat, Haryana, Kerala, Madhya Pradesh, Maharashtra, and Uttar Pradesh (West) Circles. We operate on the 1800 MHz frequency bands in the Delhi, Himachal Pradesh, Rajasthan and Uttar Pradesh (East) Circles. Under current regulations and according to the terms of our licenses, we can apply for additional Spectrum upon reaching certain threshold numbers of subscribers. For example, on reaching a certain threshold level of subscribers and traffic on our network in our Uttar Pradesh (West) Circle, we received an additional Spectrum in the 1800 MHz frequency band to operate our services.