Hi Ashok. Why to use NAVMAN ? They are not having ASIA maps package.
Go with Google Navigation, father of all Navigation companies. I suppose you must be having a smartphone. Just use any cellphone company GPRS to use Google Navigation. Monthly cost max 150 Rupees for GPRS unlimited package.
One more option is there, free offline navigation for Android devices. I use it at the places where GPRS signal is not available.