Thank You all for replying.
So in the end it drops down to either getting a dongle/wifi dongle or upgrading to Neo900 which isn't really worth it IMHO.

I had less knowledge on this and thought that 850MHz and 1800Mhz are supported by N900 and the SIM carrier which I want to use so I can some how achieve this by some soft/hardware hacking. But it seems like this is not the case as it also requires LTE modem support.

Can't we get any opensource lte cellular modem?

and for the android trick here's a link
http://vlivetricks.com/use-4g-sim-in...mobile-phones/