Indic Language Support for SDK but not PhoneGap
Check out this page of Dr. C. Scott Ananian, it could be useful for what you're trying to do. He has worked with ports of Pango (an Unicode text layout library).
enabling mobile phones with Indian scripts has been around for quite sometime. Check this out: http://code.google.com/p/indic-keyboards/
(An open source project providing an input method which will allow the usage of Indic scripts on both Windows and Linux, using Java and Unicode.)