What exactly does turning off Cell Data disable?

[RedAlert]

I recently had to reset my network connections and afterwards I was setting it back up and noticed my cell data was still off(I have been using it that way). After a few minutes I saw that the phone was on an extended network and not Sprints( I live in the boonies so nothing new there). When I arrived at work with excellent coverage, it was still on the extended network. I flipped cell data on and instantly got onto Sprints network, and also received a bunch of MMS messages and 2 voicemails that I never received from earlier in the month.

Now my question is, does cell data have to be on in order to receive voicemails, and mms? I thought turning cell data off but being connected to wifi(as I am 95% of the time) allowed everything to work

 

[bab2010]

Cellular data turn off your 3G/edge/GPRS which means that you will need wifi to be able to access Internet or be able to use anything requiring Internet connection.
But since MMS and Voice Messages a tight to your phone number, they will not come to your iPhone if you have cellular data off and wifi on. They will just be on your network server waiting for you to turn on cellular data before they can come into your iPhone. Those MMS and Voice Messages services can not arrive into your iPhone over wifi and that why you have never receive them while your cellular data was turned off.

 

[Primetime]

This is one of those you just need to keep on. Keep cellular data roaming on. However you may want to take data roaming off. I find that to be most effective.