The SMS message may get converted to MMS in the following situations:
- If Group Text is enabled in Settings > Applications > Messaging > Group Text, the responses to a group will be sent as MMS message. Disable Group Text if you don't want the messages to be converted.
- The message type may get converted also if the phone variant has been created with a setting that forces the long SMS messages to be converted to MMS. This is a variant level setting which cannot be changed by the user. By default the SMS messages are not converted but in some phone variants the conversion of long SMS messages to MMS may take place (e.g. if the fragmented SMS messages not supported in the operator network or the costs for sending several SMS messages would be higher than sending a single MMS message).
- In some Symbian phones the message type gets converted from SMS text message to MMS multimedia message if the message length exceeds the device-specific setting which is typically 5 - 10 SMS fragments (around 760-1520 characters). If the message is longer, it is converted to MMS to avoid potential issues in handling long text messages in the recipient device. The cost of a SMS message consisting of several concatenated fragments may also be higher than the cost of a single MMS message.
The conversion from SMS text message to MMS multimedia message occurs when the automatic message type is selected in the message options. This is the default mode where the device tries to automatically select the best mode for the message. The conversion from SMS to MMS can be avoided by selecting Options > Sending options > Message type > Text when in the Text message window writing the message. The message is then always sent as SMS text message and no conversion to MMS occurs.
The maximum number of concatenated SMS submessages can be up to 10 (around 1520 characters). In multimedia mode the message length can be longer.
- The message type will be converted to MMS also when sending an SMS message to one or more contacts and one of the contacts has only an email address and no phone number defined. This is independent of the number of the recipients. In order to avoid the conversion to MMS, remove from the recipient list the contacts which don't have any phone number in the contact details.