Although iPads can download apps made only for iPhone/iPod Touch, the iPhone can only download iPhone or iPhone/iPad apps. Apps made only for the iPad do not appear on the App Store. Luckily most of these apps have an iPhone counterpart such as Angry Birds (iPhone) and Angry Birds HD (iPad only).
iPhone apps work on iOS devices (iPhone, iPad or iPod Touch) they will not work on a Mac running Mac OS X 10.7 (Lion) or any other Mac OS X version
The iPhone, along with the iPod Touch and iPad, run iOS, previously called iPhone OS.
Not with the current firmware. However, iPhone OS 4.0 supports this feature and will be available for download in the summer.
No. Some apps have been ported to OSX and you can download them from the new Mac App Store (comes preloaded on all new macs, comes as a part of Snow Leopard.) But you can't play straight iphone apps.
There isn't an iPhone model called "iPhone OS". iPhone OS refers to the operating system the iPhone, iPod Touch, and iPad run. To answer the question, each of these devices are only limited by the amount of available space remaining in memory. Each application (or app) is a certain size to download and install. Typically, the size for the download is smaller than the finished installation. I do believe each app in the App Store states the file size, so that should help determine how many apps can be installed. Also, iTunes on PC or Macintosh will give a graph stating the amount of used space, and the amount of free space remaining on any specific device.
The iPhone OS 4.0 will be available to iPhone and iPod Touch owners for download through iTunes during the summer of 2010.
The official operating system for the iPad is Apple's iOS. The most current version is 4.2.1 There may be some third-party open-source operating systems that are compatible with the iPad hardware, but installing them will void your warranty.
Not exactly. The operating system of iPad is iOS (formerly iPhone OS). This is completely different (in terms of distribution) to Mac OS.
If you pay to become an Apple developer, you can install an iPad emulator on your Mac to test apps your write. This is the only way.
Not all. Apps in the Store list the OS that they support.
Adobe Flash Player is not supported on iPhone OS (iPod Touch, iPhone and iPad). In short, you can't.
You can probably download phone apps to a standard laptop, but they won't be able to run because the laptop CPU and OS are incompatible with the smartphone CPU and OS that the apps were coded for. But if you had them on the laptop and then downloaded them from the laptop to the smartphone, they would run on the smartphone.