I need to configure my N800 to show date and time in ISO format. How can I do so?

Short of hacking the timezone configuration in xterm, you can't.

Add your vote to bugs #303 and #463 in order to ensure progress towards removing this absurd restriction.

Lively discussion on this very subject in the Maemo Users newsgroup here.

I read through that discussion.. my jaw is still firmly locked in the "open" position from how badly Jakub seems to understand the situation.. so totally mis-informed by how time and date formats actually works on systems in general and how people use them.
I'll go away now and read something else lest I risk joining that list and start flaming..

I must admit I'm also pretty shocked by Jakub's laissez faire attitude, and also how sure he is that *everyone* in a given country always uses the same format - as if it's governed by law or an international standard that the US/UK will use 12hr clocks! Argh!!!! His suggested workaround (with no apparent acknowledgement of the problem) where we set our region to Germany and thus alter the date/time settings staggered me - that's fine as a temporary fix, but please acknowledge/accept this is a real problem and prioritise a fix rather than dismiss it as not a problem.

I just hope Jakub is not responsible for this component in Maemo and that someone more worldy-wise can push it forward.

Agreed..
And if you change the region you'll change also currency- and number formats too afaik, i.e. you could risk ending up with 1.300,10 instead of 1,300.10 or the other way around. Using region to change date/time format is simply not feasible, even if it wasn't just silly.

I've added my votes. I'm also going to offer the locale definition I use on Linux, as a workaround. Once I work out this whole N800 shell thing I'll give it a try.

Install xterm ... there is a N800 version in the maemo bora repo AFAIK
Install becomeroot ... the 770 version works fine
Type 'sudo gainroot' in the xterm to become root user.

That is about it in a nutshell.