If you see BOXES or BLANK, you PHONE itself does NOT support Devanagari.
You can type Hindi, Marathi, Nepali and other languages which uses Devanagari Script.
1. Goto Settings -> Language and Keyboards
2. Enable JustHindi
3. Select “Input method” -> then JustHindi
Works only if
1. Hindi Font Installed
2. Device Complex Font Rendering.
Latest Indian firmwares supports these.
All Device above 4.0 Ice cream Sand-witch.
Report any issues or requests here or mail to firstname.lastname@example.org