I got a T24 sim from big bazar the other day, it was of Tata DoCoMo, never had any idea about its network coverage and connections, it was a pre-paid sim. Fortunately, the signal coverage in my area and even at my college was decent.
But sometimes while skype chatting over 2g, even if I shook my phone a little bit, there would be a lot of disturbance. In some places there was absolute no network. Annoyed by this I ported to BSNL, which is working quite good, at least better than TATA DOCOMO.