Using 3G data when WiFi is available

Hello,

I am part of IT in a company that uses iPhones for managers etc. The question I have is with respect to data usage on their phones.

When they go on business trips, they ramp up mobile data charges (with roaming etc) sky high, however they all claim that whenever they used data, WiFi was available and connected.

I would understand if one or a few of them didn't understand when their phone used data (some didn't understand that streaming... uses wireless data), however a few are actually tech savvy and were dumbfound by this as well.

I have searched on other boards as well, and found that there is an ongoing ping pong between AT&T blaming Apple (for allegedly disconnecting WiFi when the iPhone screen "goes dark"), and Apple saying there is no situation where this would occur.

Have you had to deal with this, and if so, have you found a solution / way around it? (Other than turning off "cellular data" or "roaming data"!)

Thanks in advance!