Service for sending and receiving MMS enabled most of the subscribers by default. An exception may be only customers that have connected a long time ago, when MMS didn't exist, and since then has never changed, neither SIM card nor data plan. If you belong to one, contact support with your carrier and ask if you have enabled this service. If not, request its inclusion. It is possible you will be informed that the service connection of services through the support service is paid, in this case, ask them to dictate or send SMS USSD command to enable the service, and then dial it.
MMS may not be configured on your device or apparatus of the recipient. First of all, you should verify that this function is in both phones. By the way, their appearance about the availability of this function says nothing. For example, the Siemens C55 phone with a monochrome screen and built-in memory is less than one megabyte supports MMS (although you can send and receive only audio files, as well as black-and-white pictures of the old format WBMP), and Texet TM-B112, despite the color display, and built-in MP3 player with Micro SD card, MMS function is not equipped.
If MMS function is there, but not configured, you need to contact the service support operator and ask them to send you the MMS configuration message specifying the model. When a message comes in, open it and select the menu item destined to save the settings.
The format of the file sent by you must be supported by the recipient's phone. It is clear that to send a JPG format file to the same Siemens C55 useless. Moreover, this format supports not even all the early phones with color screens. Also important is the volume of attachments.
The standard for MMS is provided, the total volume of all the files in a single message no more than 300 kilobytes. But additional limitations may be set by the devices of the sender and recipient, as well as the operator, especially if you activated unlimited MMS sending. Often helps decrease the message size to 150 and less kilobytes.
Also possible restrictions on the mandrel MMS between operators, cities and countries. In major holidays, can not get MMS messages on an unlimited tariff, or they may still be charged. Some operators also do not support sending MMS to e-mail.
All the days of MMS messages to be sent at the unlimited rate, you can come with a considerable delay component, sometimes a few hours. It should also be noted that if you are on a mobile phone with unlimited Internet, send files, in most cases, rational-but not through MMS.