Any chance any Linux software exist that can turn the N900 into a wireless hotspot like Symbian devices using joikushop ?

http://www.joikushop.com/

should be possible

In theory that will be possible. There are some caveats though.

1) BlueTooh DUN is a viable alternative.
2) The WiFi driver has to support AP mode. The new driver is open source and supports new MAC80211 framework so is no issue.
3) You might need some terminal work or write shell script. Don't worry, people here will help with that.
4) It always drains the battery (even on Symbian or Windows Mobile or iPhoneOS)
5) You should keep in mind wireless cryptography. None of those applications such as JoikuSpot support WPA(2), and the Linux WPASupplicant has to support the WiFi driver. Probably not the case. However, you could use something like OpenVPN or IPsec.

If using Ad-Hoc mode and WEP security is enough for you, a simple script using wireless-tools should be enough to do the trick. You can use dnsmasq for providing clients with IP address.

(I assume wireless-tools and dnsmasq will still run on N900 OS).

Why is WEP enough?

since the targeted provider is T-Mobile (for US anyway), it would seem logical that the @Home hotspotting would work.

Not sure I understand what you mean. I just proposed a simple solution (I'm using it sometime to turn my laptop into a wifi "hotspot"), but I wanted to stress its drawbacks. I agree that your solution is better, but may require more work.

Anyway we'll have to wait for the device to be released to really answer the question, but i'm sure that this will be one of the first application available for n900

Someone should write Joikuspot-like program soon, its a killer app in symbian

As eber42 already pointed out, there's not much of an app to write -- that functionality is already present. One more reason I'm glad to be running an slightly-updated PDP-11 SDK on my handheld computers.

I could be mistaken, but I believe I've seen detailed instructions for setting up sharing a BT DUN link over wifi in Maemo 4; that should stay almost entirely the same for sharing the built-in connection on Maemo 5. I haven't messed with it, but IIRC you did need to run a custom kernel.

I was in fact planning on writing those scripts for myself already. I guess some simple UI frontend and a proper package would be in order.

As far as BT tethering goes 1. you need to do some scripting for that too (also planning on seeing if those could be packaged nicely) ATM 2. wifi should be faster even if will eat more power.

EDIT:

Any new people should start reading from N900 as a Wifi Hotspot, part 2 -thread.