
To start, launch Google Talk on your desktop
1. Add contacts the same way you usually do: click on the Add button to add a friend
2. Type in the phone number of the person you want to call in the following format.
Use full phone number, including country code and area code (Example: for UK, use 442071234567@talkster.gtalk2voip.com)
3. You’ll get a confirmation from Talkster with instructions. Talkster assigns a local Talkster number for your friend in their country. Your friends will use Talkster phone numbers to call-in to be connected with you.
4. If you are calling your friend on a mobile phone, he will receive an SMS with his Talkster call-in number for you. Otherwise, let him know the Talkster number by IM or email. (Source)
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