Smartphones apps transfer various types of data over the provider's data network (or wifi, if enabled). What security risks are there in this transfer, and how can the risks be mitigated? I'm not talking about cell phone security in general, but specifically the area of data transfer between the phone and some other source over the cell phone or wireless network.

Smartphones apps transfer various types of data over the provider's data network (or wifi, if enabled). What security risks are there in this transfer, and how can the risks be mitigated? I'm not talking about cell phone security in general, but specifically the area of data transfer between the phone and some other source over the cell phone or wireless network.

Edit: Sorry for the vagueness, I'll try to narrow it down. I'm wondering specifically about the channel used for data transfer (either the provider's wireless network or a wifi hotspot). What encryption (if any) is provided over these networks, and how common is it for apps to encrypt data in addition to what's provided by the channel itself? For example, what encryption is used by the Facebook app over a public wifi network? What about a banking app over the provider's data network? What about Gmail over a WPA-secured wireless network? etc.