What is the best IDE for developing a C++ application targeting Symbian UIQ-based phones like p990 and p1?
So far I have come across Carbide C++ which seems good but I am not sure if it supports UIQ (maybe it only supports S60 platform) and if it's the best option.
Carbide C++ should support UIQ, but I think you need to download a UIQ SDK separately. Not sure where you can get that today as UIQ has closed there website. Sony Ericsson used to have SDK extensions for some of their devices available from developer.sonyericsson.com
Yes Carbide C++ is the right answer. UIQ SDK availability is another story, however. After the bankruptcy of UIQ the rights to UIQ were locked down, and have not been contributed to Symbian Foundation.
As far as I know there is no "legitimate" way to get hold of the SDK. On the other hand, there is no rightsholder who will chase you down if you do...
Sony Ericsson has a UIQ archive here.
It mentions Borland C++ Builder and I seem to remember that the UIQ3 SDK also supported Visual Studio.
Do you absolutely need to be programming in C++? It should still be pretty easy to write JavaME applications for the P990 and P1.