Choose a design based on where you would like to wear your headphones. Ear buds fit inside your ear, while over the ear headphones wrap around the outside of your ears. Behind the head headphones fit into your ears and rest below the back of your head. Over the head headphones are standard.
There are two kinds of networks types: CDMA and GSM
CDMA: CDMA is predominantly limited to the US and parts of Asia. It is not supported throughout the European Union because of regulatory restrictions.
GSM: GSM is the a much more international standard and works across most geographies including the european union.
If you are looking to travel mostly inside US you should stick with CDMA because it offers a much better coverage than GSM, especially in the rural areas. However, if you plan to travel internationally, GSM might be a better option because of much broader support.
Each network type is further supported over different frequencies - also called as bands. The different bands include 800 MHz, 850 MHz, 900 MHz, 1800 MHz and 1900 MHz. Note that 800 MHz and 850 MHz are actually the same band and are used interchangeably. GSM Quad-band cell phones support the 850,900,1800 and 1900 bands and are best suited for international roaming.
Candy Bar This style of phone is rectangular in shape with no flip design features. It was designed to have the feel of a real phone, both durable and nonsense free. The size ranges in both width and length depending on the model.
Flip/Clamshell This style of phone has two parts, connected by a common hinge, which allows the user to close off the inner face when not in use; thus, the inner key functions and screen are protected.
Slide This style of phone has two plates which slide apart with pressure, unveiling the inner screen and key functions. It is useful for people who don't like flip phones, but still like the design of having two different interfaces.
Swivel This style of phone is a lot like a flip phone, but instead of opening courtesy of a hinge, it has a hinge that allows the user to rotate the top face to the side and up, in order to expose the inner face.
Expansion slots are built-in areas for future expansion. Some PDAs are made without certain features, but have built-in slots in case you want to add those features later. If the PDA you want to purchase does not have a certain feature that you are looking for, it may be expandable to include it in one of these slots.
Installed memory is the amount of available memory that comes with the PDA. While you can usually add more memory through an expansion slot, you want a PDA that has enough memory to run the programs you intend to use and to store your personal information.
Internal antennas are built into the device and can not be changed or directed. External antennas can be directed to point in different directions; this may be used to increase range of the device. Detachable antennas are screwed into the device and can be upgraded or replaced easily.