I'm surprised that in europe and united states everyone has a ringtone in his own mobile phone, I'm from mexico and i would like to know what it is the infraestructure needed to send a ringtone by a phone call, does it depends on the mobile phone provider?
Well, it requires that your phone is able to receive an SMS message. That also requires that your service provider have the infrastructure in place to support sending SMS message. That infrastructure includes an SMSC (Short Message Service Center).
SMS by the way stands for Short Message Service.
Alternatively, and this is less likely, they may support the new MMS standard. That is, Multi-Media Message Service. As you can imagine, that would require an MMSC in the service providers infrastructure. And you guessed it, MMSC stands for Multi-Media Messaging Center