Few years back I got chance to work in billing software.IMO,from newspaper articles I have read:With respect to IT in India,there are two types of jobs-developing telecom related software and all work surrounding telecom software-Billing,web-enabling and integration sofware.Majority of work falls in surrounding software.If its developing telecom related software-people might work in C/C++ with knowledge of one or more subjects-data Networks/digital hardware/communication theory/data compression/DSP/VLSI.List will quite vast I believe.Best way is to look for Career section in leading telecom companies websites.