WhatsApp is a free download for all phones, iPhones, Androids, Windows, Blackberrys, and Nokia.
Once you sync your contacts, you can see which of your friends also use the same app.
Send messages back and forth, photos and even group chat, all for free over a strong internet connection.
WhatsApp is free to use the first year you download it, but it costs a dollar a year after that.
And soon, they'll be adding free phone calls.
Viber is another great app that works in a similar fashion to WhatsApp
that already allows you to make free phone calls in addition to free texting as long as both Viber users are connected to Wi-Fi.
Line is another service that works on both iPhones and Androids and on PCs.
And again, all you need is a strong wireless connection and you've got service.
And that's what makes this app so useful when you're traveling abroad.
There's no need to change your mobile plan.
Before you go, just make sure you can connect to free Wi-Fi and you can communicate with friends and family easily and for no charge.
In San Francisco, I'm Kara Tsuboi, CNET.com for CBS News.
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