The iPhone 4 has been in high demand since its release in June, selling well over 1.5 million devices in its first three days of availability. But supply is still short, especially with expansion into the overseas market. According to AppleInsider, mobile carrier China Unicom was only able to meet about half of the pre-orders placed by customers, with the rest having to wait until the end of October for their orders to be fulfilled.
Similarly, the iPad suffered high shipping times upon its release in April, with things only improving in August when Apple's standard shipping time of 24hrs was reached.
In the UK, the iPhone 4 shipping time is set at three weeks, while the iPhone 3GS can be shipped in one to two weeks, according to Apple's UK online retail store.
Personally, I've currently got an iPhone 3G with the mobile carrier O2. The contract has expired, and I'm now running on their Simplicity tariff. I could upgrade to the iPhone 4 with O2 (they seem to get priority stock), however, Tesco is offering the most cost effective contract (for me anyway). Unfortunately, though, they never seem to have any stock.
Tesco is offering a 16GB iPhone 4 on a 12 month contract at £35 a month. The upfront cost is £229, but the overall cost of ownership is £649. With this contract, you get 750 monthly minutes, a 1GB monthly data allowance, and unlimited texts. Alternatively, O2's £35 a month contract is for 18 months. The upfront cost is cheaper, at £179, but the overall cost of ownership comes in at a much steeper £809. Worse still, with this contract you only get 300 monthly minutes and a 500MB monthly data allowance. If I was to purchase a contract nearer the 600 minute a month point with O2 (which is more like what I need), I'd have to pay £40 a month on an 18 month contract with the overall cost of ownership being £839.
For me, it's obvious to go with Tesco's iPhone 4 contract. Unfortunately, until stock supplies improve, I'm forced to hold onto my iPhone 3G.
Engadget has done a fantastic comparison of all the price plans for the iPhone 4 in the UK. If you haven't got an iPhone 4 yet, and you live in the UK, it's well worth the read.