Let's take a look at auto redialing, why it is not openly allowed on your iPhone, and what options you do have.
Auto redial is a function that allows you to continue returning phone calls if you receive a busy signal on the other end, or simply to continuously call a number. This auto redial feature has been used by commercial institutions for a long time to make long strings of calls to the same number, and now on the iPhone this function seems easily resurrected with an iPhone app....or so you would think. This feature is not something that can be done easily from the iPhone because of the design of the iPhone's iOS, but there are options for redial. Here is a look at why the iOS does not allow Auto Redial, what options you do have, and if you can do it with a jailbroken iPhone.
The iOS actually blocks functions like this because of the GUI. On a more manually functioned phone it may be possible, but there is a distance between the iPhone's calling features and the software that may perform this. This would also be difficult with the expensive phone plans from AT&T and how few mintues most people have. There is really no way that you can initiate a phone call from the iPhone without actually making manual selections for that call, which is the premise on which auto redial is based.
If you simply want to redial and call someone back you do have several options that will save you time. If you just press the Call button in the Phone section the last number you had entered will come up, and you can just press Call again to make the call. You can also just go into Phone and go to Recents, then select the top number. If you think that you will be redialing this number regularly then you may just want to try putting it into your favorites list so you will have easy access.
Jailbreak Your iPhone
Jailbroken iPhone's will give you options that the restrictive hands of AT&T and Apple would never allow. What happens here is that iPhone app developers are not restricted by the iOS in the same way and do not have to get approved by the iTunes App Store. This opens up the possibilities for auto redial on your iPhone, though the options are still pretty slim at this point. Xtension Mobile Log 4.0 asks that you have an iPhone 3G or 3Gs, update to iOS 4 or iOS 4.0.1, jailbreak, and then utilize Cydia to install. Once you do have Xtension Mobile Log 4.0 available, which costs $9.99, then you have a whole host of different calling options like auto redial and changing different call log screens. Xtension Mobile Log 4.0 is one of the only packages that is going to allow auto redial on the iPhone, but it requires a whole lot, is relatively expensive, and has a lot of other features you may not actually want. Still if you want an auto redial iPhone app this might be your only option.