Download settings for Internet and MMS. If downloading doesn't work, enter the settings manually.
Check the signal strength in the status bar to make sure your device is connected to a network. If the signal is weak or you have no signal, move to an open location free from obstructions, or get close to a window.
Check the device memory and memory card to see if memory is available. If the memory is full, remove messages to free up space.
Use the full phone number when you send a message. When you enter the country code, use “+” instead of “00″. Touch and hold “0″ to add a “+”.
Try the previous steps again, but with another SIM card. This is to determine whether the problem depends on the SIM card. Preferably use a newer SIM card which meets the specifications of your phone, for example, use a WCDMA SIM card with WCDMA (3G) phone. If your phone is locked to a specific network operator, use a SIM card from that operator.
Back up all your data saved on the device, and then perform a factory data reset.
Update the device software to the latest version / repair the software using PC Companion (for Windows® computers), or Sony™ Bridge for Mac (for Apple® Mac® computers).
Contact your retailer or a Sony Mobile repair partner. Before handing the phone over for service, back up all your data to avoid possible data loss. Data on the device may get deleted when examined. Don't forget to bring proper documentation, for example, proof of purchase and warranty card. The documentation required may vary depending on market, country or region.
