You may also want to look at what's eating CPU, and maybe taking some time to re-flash the device and install stuff anew. If it wasn't doing this a year ago when you got it (pausing several seconds on phone ring), then it's something you've added or changed that's causing it. One of the best parts of the N900 is that you can flash it on your own with older images or current images and re-install it without going to a shop.

I haven't had to reflash mine in the 16 months I've had it, but I also limit what I install and test it out on occasion to see if a changed setting is hurting it. (I also know a bit about linux optimization and know how to look for buggy/leaky programs. )

It could be the "new phone" you're looking for is right in front of you. It just needs a good cleaning out and detailing.