Inter-operator SMS messages can be further divided into two categories -- local inter-operator SMS messages and international inter-operator SMS messages (international SMS messages). A local inter-operator SMS message is an SMS message that is sent from one wireless network operator to another wireless network operator in the same country, while an international SMS message is an SMS message that is sent from a wireless network operator in one country to a wireless network operator in another country.
Usually the cost for sending an international SMS message from a mobile phone is higher than that for sending a local inter-operator SMS message. Hence, the cost for sending an intra-operator SMS message <= the cost for sending a local inter-operator SMS message <= the cost for sending an international SMS message.
The interoperability of SMS messaging between two wireless networks locally and even internationally is undoubtedly a main factor that contributes to the success of SMS worldwide.
Source Article : http://www.developershome.com/sms/
