SMS messages are transferred between mobile phones via a Short Message Service Center. The SMSC is software that resides in the operators network and manages the processes including queuing the messages, billing the sender and returning receipts if necessary. Many operators now offer web based interfaces to their SMSC so we can send short messages to any mobile phone from the web. Some websites now offer free SMS.
Available bulk SMS providers all over the world:
TAP/UCP Dial-up SMS Providers: