Yes, I mentioned that in an earlier post in this thread. But, for me it would be more fun to use usb stick modem and play with the software!

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/

Well, it is a piece of HW, not SW so the question is a bit off I think

Or to be precise, the modem can be a separate chip or part of the SoC (built on the same chip as the main CPU)
The modem baseband part runs its own firmware, which is a RTOS variant (or rather, very dedicated O&M loop with some very simple OS operations...)
This firmware is very much propriertary SW owned and developed by the chip vendor and is not opened.
There does exist some limited (meaning, just 2G functionality) open-source implementation of the GERAN stack but even that only supports some very old modems not an longer on the market.

Well, I was talking of HW thinking that we could fit a seperate lte modem inside N900 but you explained the difficulty very well.
So I'll be better off with some cheap prepaid 3G internet or a 4G modem to use with the kali linux