Operating Systems of PDAs of the TIme

Heard of new age OS for your PDA like Symbian, BlackBerry OS, Windows Mobile and iPhone OS. and next generation Google's Android, new OS for PDA. Most of the PDAs are working on Push technology, which ensures prompt delivery of mails. On the context of ne wgeneration PDAs, many apps are aviable on PDAs like
Opera Mini 4.1 - a popular web browser:
Consilient Push- a push mail client with mobile phone with data services;
Gmail App-Gmail version avaialble on mobile phones;
Nimbuzz-allows you to chat thru the contacts from Gmail, Yahoo and MSN;
Google Maps- It is free. I know many serivce providers are avialble on payment but hti sis free on your PDA(need more time to work in India)
while we have many OS are avaialble for PDAs, most of the instrument providers are Nokia, Black Berry, HTC and Iphone and many more.
These PDAs with all these apps are helpful to run the business without disruption.