I managed to get my hands on an iPhone 3G a couple of days ago from Eurotel (O2) in the Czech Republic, its the 16GB Black model and I thought Id share a few impressions here after having had some time to use it.
First of all, in terms of ease of use, its exactly what you would expect from an apple product and has been easier to set up than most of the other phones that I have owned for other things besides basic calling.
When you first open the box and take the iphone out, you will need to put in a sim, if you are using a pre-existing sim of your own, then its a good idea on your old phone to switch off any PIN's that you have set and also copy across any numbers stored on your phone to the sim card or sync your phone with your computer to its address book. I did the second option and synced my Sony Ericsson with isync on my macbook pro to my address book and then afterwards sync the address book to the phone via itunes.
I'm getting ahead of myself a bt though, once the sim is in and you have powered on the phone, you will need to connect it to itunes, on the first connection it will check if there are any outstanding firmware updates and if there are, it will download and apply them. This happened to me and I needed to download a 250mb file (largest firmware update ever?) which took around 15 minutes and then afterwards the phone was "stuck" on the progress bar for around 10 or 15 minutes while it did its stuff, afterwards it rebooted, connected to iTunes and I was able to configure what I wanted it to sync.
So far in terms of syncing I havent experienced any issues but the phone does make a backup of itself before every sync and if a lot of things have changed, this can take a few minutes, there are methods to turn this off though (via the terminal) if it frustrates you, for me, for the most part I tend to sync my phone/ipod at the end of each day ready for the next, so I prefer to have a backup.
Calling via the phone works pretty much as you would expect and quality is good, either via the external headset or the built-in speaker and microphone, so nothing too exciting there but nothing to complain about either. The headphones also have a mic on the end that doubles as a remote control for the ipod/phone so you can accept and receive calls with it or pause/play/skip tracks without having to take the phone out of your pocket.
Ive only had it for a short while, so I am still playing with it but I will post some more comments up later.