Help in the selection of BlackBerry ?

Just get an iPhone.

If you're looking to purchase a BlackBerry, there are several form factors you get to consider (unlike the iPhone) and it's certainly worth shopping around for. Of course, each carrier offers a different line up of BlackBerry SmartPhones, so consult online to find out which cell phone carrier offers which models of BlackBerrys.

All BlackBerrys offer a keyboard, either a full QWERTY, 20 key, or virtual keyboard, come with software to sync with your computer, and require a data plan with all US cell phone carriers. Currently the line up looks like this:

AT&T: Bold (9000 and 9700), Curve, Curve II, and Pearl
Sprint: Tour, Curve, Pearl II.
Verizon: Storm, Tour, Curve, Pearl
T-Mobile: Curve (8900 and 8520), Pearl, Flip.

These lineups are current, but of course, subject to change.

Picking a BlackBerry really depends on what you consider to be your perfect phone. Do you want something slim and pocketable? Try a Pearl or BlackBerry Flip. Do you want a bigger screen but still want an actual keyboard? Curve, Curve II or Bold. Bigger screen than those, but are OK with a virtual keyboard? BlackBerry Storm

Take the time to visit each provider and see which phone fits the best, and shop around online for the best deal in a cell phone.

This really depends upon what you want to be able to do with the phone? It also depends upon the service network that you have. Maybe you can put another question up with what you are needed the phone for, and what provider you use.