I just couldn't stand the speed of iOS4 (or iOS3 for that matter) on my iPhone 3G any more.
Thankfully, my Optus plan was over, so getting a new phone was a no-brainer and, after seeing the iPhone 4 and its sexy glass and stainless-steel surfaces, how could I resist?
You see, my primary requirement for a phone, above everything else, is that it has a glass or sapphire-coated screen. When in my pocket, the screens of my phones get quite scratched up and I detest phone cases, so the screen needs to be as scratch-proof as possible. When it comes to the smart-phone market, Apple is about the only game in town when it comes to glass screens. And now, with the new iPhone 4, I get a glass back as well!
Another point of pain for me over the past two years is the Optus network. Whilst I understand that before the iPhone 4 the Optus network didn't support the 900MHz range however, given the similar issues I've had with Optus over-subscribing their network via my 3G dongle I just didn't want to chance it again. So, to cut a long story short, I ported to the Telstra network (on a plan cheaper than my original Optus plan anyway... the tribulations of being an early-adopter).
My experience with the new iPhone 4 and the Telstra network have been stellar. On the Telstra network I have connectivity everywhere, including parking garages and bathrooms (yes, eww). It's fast (much faster than the Optus network ever was) with extremely low-latency. Additionally, I can't replicate the antenna problem the iPhone 4 is meant to have with any consistency. In the worst case, I drop a couple of bars but, on the Telstra network at least, this doesn't affect call-quality or Internet connectivity.
The iPhone 4 itself is a big improvement over the iPhone 3G. In fact, it even appears faster than my iPad 3G (also on Telstra), even though it should have the same CPU. iOS4 or the 512MB of memory might be contributing to this speed-boost. Especially applications that support "multi-tasking" well like the Facebook and Twitteriffic applications. It's also nice to get an extra 20-30% out of the battery during the day and I haven't managed to run it flat yet.
Anyway, I would highly recommend both the iPhone 4 and Telstra networks to anyone coming out of their contracts. I know the new Optus plan is very temping however, do you really want to put yourself through the same crap again for the next two years for the sake of $20-30 per month?