Hi

My question is if a blackberry has both WIFI and 3G enabled, which network is used to connect to the Internet ? Is it possible that any user app can establish a network connection and transfer data over any (WIFI or 3G) network at will, assuming both the networks are available.

Depending on your setup the BB can switch between both depending on availability.
the WiFI profile can be set to use either a cell source or local WiFi.

Thanks for the reply tsac. But can you clarify that if both 3G and WIFI are available at a given instance of time, an APP can choose either 3G or WIFI as the connection medium. I know on Android and Apple, if WIFI is enabled all the APPs use WIFI only. I want to confirm that Blackberry differs in this behavior.

Yes, an application developer may write the program to use what ever connection method s/he may wish (depending on user permissions and IT Policies of course). Depending on the OS BIS and BES will go via Wi-Fi when available so apps that use BIS-B or BES connections will do so as well.

That said, the easiest way to write a connected app is to not specify any particular connection and let the device choose, in which case it will behave the way you describe Andooid and iOS devices.

Thanks for reply 'hrbuckley'. Extending my question, is it possible to determine programatically how much data has been consumed over WIFI and how much data has been consumed over 3G.

No, it isn't really. Some programs make a stab at it by keeping track of how many bytes are sent/received while each connection method is available. But since an app doesn't have to use Wi-Fi just because it is available, they usually diverge from valid numbers over time.