Hi Esma
You have to register on phones.com, pls visit:
phones.com/accounts/register [phones.com] and receive $0.5 free Credit to use with our Callback service and/or SMS Service. You would be able to send SMS to your friends worldwide, its cheaper than other SMSing services. In future, you can also buy SMS credits, please have a look at :
Bye SMS credits [phones.com]