Q: If my iCloud settings are switched off can I send or receive iMessages or will they go through as text messages?
A: Your iCloud settings, found in the iCloud section of the iOS Settings app, are completely independent of your iMessage settings.
You can use iMessage even with iCloud completely disabled, or even if you’ve never setup an iCloud account at all. If you’re on an iPhone, you don’t even need to sign in with an Apple ID if you only want to send and receive iMessages using your cellular phone number; an Apple account is only required to associate email addresses with iMessage. FaceTime works in the exact same manner in terms of phone numbers and Apple IDs.
In fact, even if you are using an Apple ID for iMessage and/or FaceTime, this does not need to be the same Apple ID that you use for the iCloud account on your device, nor do the iMessage and FaceTime services require that you use the same Apple ID for each other. This also holds true for Game Center and the iTunes Store. While most people use the same Apple ID for all of these services to keep things simple, you are by no means required to do so, as each of these features operated independently of the others.
For more information, be sure to check out our Complete Guide to FaceTime + iMessage: Setup, Use, and Troubleshooting.