How do I cacel my data?
Go into settings, data usage, and turn the mobile data from on to off. That easy but don't be surprised if the darn thing still uses data on the background apps already installed in it. then you would have to go into the apps settings and turn off what ever apps are running in the background
Smartphones require data plans. You could try to downgrade your amount of data if your line is eligible. This would save money but I do not believe you can just use a smartphone for calling as texting/MMS also uses data services.
I'm sorry, I thought you were asking to cancel data services, not turn off the mobile data. Holiday44 is correct in that regard.
And keep in mind if you turn cellular data off, there's a lot that may not work. You can go down the list and pick and choose what to turn off.