There are different ways to keep in touch with friends and family staying in the United States or in some other country. But, texting or calling their personal phone stays above any of those ways. While we are not discussing about calling here, we will provide you with a invaluable tool that lets you text your friends in the states (or most other countries too) for free.
The tool is Pinger’s Textfree. You can use Textfree from the web, or from your phone (app available for iOS and Android). When you sign up for Textfree, you will be allotted a US mobile number using which you can send (and receive) unlimited number of text’s to any supported number in the world (including USA).
Since you are being allotted a US mobile number, you should use the respective country’s code (including the plus sign, for example, +91 if you are texting to a mobile in India) before the mobile number itself, when texting a phone outside US.
Remember that when the other person replies to your message, he/she will incur International SMS charges as per their plan. In case the other person is US based with a US mobile number, he/she will incur normal local texting charges. For example, let us assume that you are texting John (who is subscribed to ATT Unlimited texting plan) from your textfree number. If John replies to your text, he would not incur any additional charge since he is already subscribed to an unlimited plan. In case John is not subscribed to unlimited texting plan, he would incur 20 cents per text (current ATT charge).
One thing with Pinger (and I suppose with other companies too) is that if you don’t use their service for a month, your number gets cancelled and you will need to register again and take a new number.
Update: Pinger was one of the first companies to provide international texting for free. Right now, there are so many other options (such as Heywire, text plus etc) to do the same.