switch wifi to 3G?

[jiggy1965]

For outgoing mail server I've entered the smtp address of my iphone provider (vodafone). Which works fine if I'm on the vodafone mobile network. But what if I'm at home or some other place with wifi? For example, when I'm at home my iphone will find my wifi and automatically connect to it (after I press 'ok' and enter the password). Which is fine. Won't costs me mobile network time/data, it's faster, free, etc. But now I want to send an email on my iphone and off course it won't do that cause I'm now on the wifi network and not on vodafone's 3G mobile network. So it won't be able to use vodafone's smtp address. I would have to leave my house far enough for my iphone to loose the wifi connection and return to 3G so it can send the email. Isn't there an easy way to switch back from wifi to 3G for a moment so I can send the email and then switch back from 3G to wifi?