How is the Blackberry Technology Different?

What is the difference between these cell phones and the conventional cell phones? There is a package called the Blackberry Enterprise Server, that is available for Microsoft Exchange, Novell GroupWise and Lotus Domino. In organizations with a large number of Blackberry PDA users, BES is used to provide undisturbed email facility to the consumers. Individuals however, can use the email facility provided by their service provider. But most importantly what make Blackberry different from the conventional cell phones are, the Blackberry APIs that are available for writing programs by any individual. You can use these APIs and write your own software. You can run these softwares in your Blackberry cellphone or PDA. However, you need to take a digital signature from the RIM before putting in this software for use by any other person.