You could ask to try a Desire for a day or 2, but I'm not sure if they'll do that unless they have a demo model lying around.
Over here (Belgium) you can buy something (anything except for underwear really) and if you don't like it you can return it within 7 days and get a refund. Don't they have a similar system there?
As for the perfect phone for you ... how important is the touch screen feature and the "smartphone" label?
You know the Experia by now, so I don't think I have to waste any more words on that one.
The Desire may be a bad choice in the kind of area you live in (it's hard to tell people not to buy one because I absolutely love mine, but I'd rather be honest about it's commonly known problems).
The iPhone ... well ... Overpriced and overhyped really.
The Sony Ericsson Satio would be an option, but they also have problems. It's said to be the spiritual successor to the C905, but that has more to do with the camera than with the rest of the phone. Like all smartphones, the "phone" function seems just an afterthought.
In fact I wouldn't recommend a smartphone at all if the call quality and reception is that important.
I would recommend ... a C905
. No, really, I do.
Sorry about that, but it has good audio quality, an excellent volume and will probably still have reception even if you were on the moon. And it has plenty of features. And the battery wil last 4 or 5 times longer than any of the phones mentioned above.
Yes, the user interface is so 20th century and the screen is small compared to today's phones. But that doesn't stop me from using my C905 almost as much as I use my Desire.
All in all : Try the Desire, but ask to try a demo model at your place first because of the reception problems. Or look for someone who lives nearby and has a Desire. From whereabouts are you? Maybe someone in the forum lives close to you.