In India, you can find a public STD/ISD both almost on every street. But you cannot find them in USA. It is not possible to make a domestic or international call in USA unless you have a mobile phone with that facility. Even if you find some public phones, it may be possible to make only a local call. So you have to choose a way to make your phone connected once you reach there.
1. Calling cards
Calling cards are the cheapest and easiest option for short duration of travel. You can purchase one at the airport in India itself and activate it once entering USA.They are similar in appearance to a SIM card and will have fixed talk time (eg.1000 minutes) for the specified duration (eg.1 month). Matrix is the popular provider of calling cards in Indian airports. If you want to buy the card in USA, then the popular and most used ones are Amantel,Keepcalling, Zaptel etc
2. International roaming with existing carrier
Most of the popular carriers in India like Airtel, Vodafone etc offer international roaming facilities. If your phone supports the GSM band 1.9GHz and 850 MHz bands, then you can enable international roaming in your phone. But the roaming charges are very expensive in almost all carriers.If you are travelling on business purpose and you cannot change your contact number, then you can use this option.
3. Renting a SIM card
You can rent a SIM card from the local carrier in USA like AT & T, T mobile etc if your phone is a tri band or quad and supports the GSM band in USA and it should be an unlocked one.This option is good as there is no roaming charge.You can copy the contacts to your phone memory so that you can use it easily. KeepGo is the popular provider in this service.
4. Renting cell phone
If your existing phone does not support the GSM band in USA, then you can choose the option of renting a cell phone. There will not be any problem in the network coverage as you are using the local carrier. You can rent a phone by visiting any of these websites Rentcell,Amigo-US,TripTel etc. But renting a cell phone is expensive than renting a SIM card.
5. Renting mobile Wifi or MiFi
Renting wireless internet access or mobile hotspots is another way for making international calls and it has the additional advantage of accessing internet. You can make calls using Google voice,skype etc. XcomGlobal is the popular company providing MiFi hotspots and it has various package plans with the most popular one being the daily plan where a flat rate is charged every day.
6. Travel packs from mobile carriers
Some carriers offer travel packs so that you can use your existing phone. But it may have some limitation like less talk time, limited web surfing etc. It will be useful if you are on a very short duration. You can check with your existing carrier in India about the details.
7. Prepaid SIM cards
If you are staying for a longer duration, you can buy a prepaid SIM card from the local carriers in USA like AT & T, T-mobile etc. It offers a fixed talk time every month and you can refill it whenever needed.But your existing phone should be unlocked and supports the GSM band in USA.Choose the carrier which offers and more talk time in the location and better connectivity in the location where you stay.
8. Buying a Travel/International cell phone
If you are a frequent traveler to USA or many countries, then buying an international travel phone will be the best option.You can use this type of phone in more than one country.Mobal is the popular provider of this type of phone and the advantages are no monthly fees,no minimum usage or contract. You have to pay only for the call you make.
9. VOIP Phone
If you are staying for a longer duration in USA, then you can buy a VOIP phone and make calls using that using the internet connection.Vonage is the popular VOIP service provider in USA. You can pay a fixed charge every month and make unlimited calls to India and other countries.
10. Pay Phones
Pay phones are similar to the STD/ISD booths in India where you have to pay the money in the box and make calls.But pay phones are becoming unpopular and only available in limited places in USA.