This is Info On The Web's (IOTW) guide to buying PDA / Mobile Devices.

Mobile Devices, also known as PDAs, come in different brands and operating systems. The 4 popular operating systems are 1) iPhone 2) Blackberry 3) Palm and 4) WindowsMobile from Microsoft. It can be confusing. With this guide, we will try to make it simple.

The short answer is buy a device with Windows Mobile operating system.

The longer answer:
There are 3 levels of PDA usage:
Level 1 - the basic functions including 1) Cellphone 2) Email 3) Calendar 4) Music 5) Web Browsing.
Level 2 - PDA size web pages to run programs and applications.
Level 3 - Create PDA applications that run on the PDA. This is especially important if there is no web connection due to location, and other factors.

All 4 PDAs listed above should function fine for level 1 and level 2 duties. But since not having constant web connection is a fact of life for now, level 3 solutions enable users to view and input on their PDAs when there is no web connection. Info On The Web creates level 3 applications only for WindowsMobile PDAs because of their capability and the support from Microsoft. That is why we recommend PDAs with the WindowsMobile operating system.

If you already have a non WindowsMobile device, such as iPhone, Blackberry and Palm, level 1 and level 2 applications should work fine.