Well, there are basically two factors that may help you determine if a mobile phone will work with cellular operators of another country or not. Here they are:
1. GSM and CDMA are the two most prevalent standards in the mobile world. As a first step, determine the technology (GSM or CDMA) used by the mobile carrier of the foreign country where you are planning to use your phone.
Wikipedia has dedicated sections – see pages for India, Europe and Asia Pacific countries – that list the standards used by various carriers of a particular country. If that carrier is on GSM, you would need a GSM-compliant mobile phone and the device should be unlocked meaning it should be able to accept SIM cards of other carriers.
2. The other important factor is the frequency band that carriers are using in the country where you are travelling to.
For instance, mobile networks in India use the 900 MHz and 1800 MHz frequency bands while GSM carriers in America operate on 850 MHz and 1900 MHz frequencies. Thus, if you are planning to buy a mobile phone for use in Usa, the phone should support the 850 / 1900 MHz frequencies.
You can use the Phone Finder database to determine the 2G and 3G frequency bands that are supported by your mobile phone. Then check the mobile operator’s website (or Wikipedia) to determine the frequency bands they are using for their 2G and 3G networks. If the frequencies match, your phone should be compatible with that mobile network.
One more thing no one have mentioned here is, Make sure to activate that device with a US Sim card. Means put a US Sim card in, and use if for like 10 minutes. And than use any Sim card either its Indian or foreign.
