HTC Desire HD unlocked, cannot connect to 3G
AT&amp;T uses 3G frequency bands 850 MHz and 1900 MHz.  From what I can tell from the phones they sell, Tata Docomo uses the 900 MHz and 2100 MHz 3G bands.  They're not intercompatible.  Most often when you buy a US phone for use outside the country you'll want the T-Mobile version. Or a quad-band or 5-band phone which would eliminate the problem altogether.