BY default android will convert longer SMS to MMS (the length could vary by phone, language and service provider). This could cost you more money if you are sending SMS frequently.
Solution change configuration of default application
In order to stop converting SMS to MMS in android do:
- open your default app - Messaging
- go to More - next to new message button
- Select Settings
- Tap Advanced
- Tab Create mode
- Select Restricted
Solution install new app
If the previous option is not working for you you can try another application like:
Then you need to open the new message app - Messages. You'll be asked if you want to set is as default. After this you can use it and send longer SMS.