Your phone issue is sod all to do with multitasking, its simply that the phone app on the iPhone is featureless. I'd not noticed before, as I tend to put the number into notes (assuming it was withheld/blocked) or tasks (if time sensitive), then call back at a time convenient to me. However, a quick play does show you can add a call whilst listening to VM, then close the VM call, leaving other one open. A bit naff though. But, as said, the phone app is
shit just about adequate.
I have no loyalties towards crApple. Quite the opposite, as you may have noticed. I use one as it works for me. I'm not tied to any silly contracts, so can change phone tomorrow if I so wished, but currently there is nothing else that meets my needs, except a later gayPhone, and I see little benefit in that.
Multitasking is the capability to run multiple threads (smallest unit of code execution) seemingly simultaneously. Of course the iPhone can multitask, as can just about any other smartphone ever made (I'd have to double check Symbian, I think that could only do cooperative multitasking). It would be a waste of time having multicore chips if the OS couldn't utilise more than one core

. If I'm out for a walk, I frequently have the iPod app, Map My Walk, the geocaching app and often a navigation app like google maps open all at the same time... ...whilst making a lot of use of Siri (which I've (reluctantly) grown to love, despite its hilarious, frequent cock ups). Thats multitasking.
So, we've established that the iPhone's phone app is shit, which we already knew. We've established that the device can multitask "OK" if coded correctly (some apps just park themselves in the background, but don't execute until they are brought to the foreground). We've also established that some people have rose tinted memories of the piece of junk that was the UK spec'd N series such as the N95, and the totally hopeless N97. (Nokia did eventually release firmware updates to fix a lot of the stability problems, and fix some of the broken features, but UK operators dumped the devices too quickly, hence the updates never came to the UK (officially, obviously there were workarounds)). However, if a N9x meets your needs, you've found your next phone, and won't need an expensive contract

Symbian released touch after iPhone and Android were launched. Like Gooseberry, they realised too late that it was a necessity. Can't think of a Nokia phone that used it though. Actually, can't think of any phone that used it. Who would? Surely you'd use the (then free) Android, rather than pay for the lesser capable Symbian, and have higher development costs getting it to work with a device.