What can an iPhone do that an Android cannot? Is iPhone worth to buy? Anybody can help me? I'm planning to buy one iPhone this fall.

The operating system of the Apple IPhone is so much different then the Android, it may be difficult to get used to. It may take long enough that you may grow weary and dislike the choice. I would stick to what you know. Besides, in my opinion Android is far superior to Apple in many ways. Android has been offering the same features on their platform that Apple considers "new" so do your research.

The best place for someone to buy a Nexus One is Nexus One Phone - Web meets phone.. The 2nd best is probably eBay. I've not heard of many others. xda-developers.com does have some phones being traded for other phones and a few being sold.
I used the G1 for a few weeks and was fairly impressed, but you would need a data plan.
Personally I traveled in Asia with my Nexus One and had data turned completely off for a few weeks. It was not a true Android experience and wouldn't really suggest buying an expensive data intensive phone without a data plan. But that is MY opinion and it is worth what it costs you.
Thanks

The iphone five will most likely be announced at apples fall conference. Most likely September 7th.

http://www.ibtimes.com/articles/165411/20110619/apple-to-release-iphone-5-on-september-7-will-come-pre-loaded-with-ios-5-android-nexus-g-competition.htm

Hope this helps!

I think you are looking to "Tether" your Android Smart Phone. To do so I would recommend buying/downloading Easy Tether Pro off of the Android Market. The App comes with detailed instructions and is well worth the cost! Just make sure you have a data plan that will allow the high traffic!

The iphone is uninsured unless you have it under your homeowners/ car insurance, ect. You should contact Apple if you have the iphone protection plan. If you do then it will cost a significant amount less then buying a new iphone. If you didnt purchase the protection plan then you will need to buy a new iphone. Check if you are eligible for upgrade or early upgrade for a discounted price before you do though.

Try going into your phone shop and asking them if they can upgrade it for a good price rather than buying a new one that has the internet. If they dont then maybe buy a cheaper phone that has internet or keeping ur phone and seeing if they have any wireless plug ins to plug into ur phone to have the internet. Otherwise you may have to buy the newer phone. Hope that this is helpful to u!