Iphone 4s text & MMS problems?

I just bought a iphone 4s unlocked & on simple mobile i got my old 4 to do it by going to general & network & cellular data thing, But this 4s only has a data roaming thing & personal hotspot but no place to edit text & MMS

To enable MMS, you have to follow these steps.

1. Open up your Settings
2. Select "Messages"
3. Scroll down to SMS/MMS and make sure MMS is selected as "on"

Go to your Messages app and see if you can MMS to an email address/phone number. If not, talk with your carrier and review your plan.

Your second issue is a mystery to me. "Editing text." Do you perhaps mean the message field?