Now you can get unlimited plan of internet from your Reliance Netconnect USB at just Rs 800 Plan. The most important fact is that roaming is free in reliance netconnect.
If you go for other usb internet service provider, some service providers will not give free roaming all over India, some plans have monthly fixed charge, some plans require post paid connection, some service providers are not providing good speed, some service providers have restriction on data transfer, some service providers are not having network in all over India.
So from above points of view, Reliance Netconnect 1x unlimited plan is best option to chose for usb internet. You can find its coverage at almost all place in India, you can also use prepaid connection, make it lifetime valid with Rs 799 (or lower), and use internet whenever you require it by refilling amount of Rs 801 from Netconnect Prepaid Data Vouchers. There is no monthly rent or anything else.
Its speed is also good. There will not be any hidden cost.
In Kerala and Tamilnadu, Reliance Netconnect 1x unlimited plan is available at Rs 600 only. You can expect Rs 600 per month in your area soon.
Remember that unlimited data use means it should not exceed 10 GB per month. More tariff plan is given here