Can the iPad models be used as an external display for a Mac?

Officially, the iPad models cannot be used as an external display for a Mac, but as first spotted by Gizmodo, there is an iDisplay application that essentially "fakes" using the iPad as a second display on a Mac via a VPN server.

What is the viewing angle of the iPad models? Is the screen visible from the sides or does it have to be held immediately in front of one person?

The original iPad models -- the iPad (Wi-Fi) and iPad (Wi-Fi/3G/A-GPS) -- and the iPad 2 models -- the iPad 2 (Wi-Fi), iPad 2 (Wi-Fi/GSM/A-GPS), and iPad 2 (Wi-Fi/CDMA/A-GPS) -- have a 9.7" IPS LED-backlit 1024x768 display (132 ppi).

The iPad 3rd Gen models -- the iPad 3rd Gen (Wi-Fi Only), iPad 3rd Gen (Wi-Fi/4G LTE AT&T/GPS), and iPad 3rd Gen (Wi-Fi/4G LTE Verizon/GPS) -- have a 9.7" IPS LED-backlit 2048x1536 "retina" display (264 ppi).

All iPad models have a viewable angle of 178 degrees horizontally and vertically, which makes it quite possible for more than one person to view the iPad display simultaneously.

Do the iPad models have a camera? Do they support videoconferencing?

The original iPad models -- the iPad (Wi-Fi) and iPad (Wi-Fi/3G/A-GPS) -- do not have any kind of camera -- still, video, or webcam, and as a result do not support video conferencing.

All subsequently released iPad models have dual video cameras and shoot video and still photographs as well as support video conferencing via applications like Apple's own FaceTime as well as Skype.

Can you make phone calls with the iPad?

No. The iPad models do not have the capability to make mobile phone calls. It is possible to use a VOIP application, like Skype, however.

Do the iPad models support Bluetooth?

Yes, all iPad models support Bluetooth.

The original iPad models -- the iPad (Wi-Fi) and iPad (Wi-Fi/3G/A-GPS) -- and the iPad 2 models -- the iPad 2 (Wi-Fi), iPad 2 (Wi-Fi/GSM/A-GPS), and iPad 2 (Wi-Fi/CDMA/A-GPS) -- support Bluetooth 2.1+EDR. The iPad 3rd Gen models -- the iPad 3rd Gen (Wi-Fi Only), iPad 3rd Gen (Wi-Fi/4G LTE AT&T/GPS), and iPad 3rd Gen (Wi-Fi/4G LTE Verizon/GPS) -- support Bluetooth 4.0.

How much internal storage do the iPad models have? Can storage be expanded? Does the iPad have a MicroSD slot?

All iPad models have either 16 GB, 32 GB or 64 GB of storage which cannot be expanded.

No iPad has a MicroSD slot. For readers not familiar with the MicroSD standard, it is a tiny flash memory card -- "about the size of a fingernail" -- designed for mobile devices to hold "music, movies, video clips, pictures, ring tones and more". For more information regarding the history of the standard, please refer to PhoneScoop.