Will the unlocked 256GB iPhone X work with its FULL features with Straight Talk service (which uses the TracFone SIM card)? My iPhone 6S Plus could never receive visual voicemail. I don’t want to spend another $1000 and find out it’s not fully compa

Visual Voice Mail is a carrier feature.

If the carrier did not support it on an iPhone 6s Plus, unless something has changed, its unlikely to be functional on an iPhone X.

As Straight Talk if they now support Visual Voice Mail.

You have to make sure that StraightTalk supports visual voicemail. If they don't; you either won't be able to get it, or you need to switch carriers. Contact them and ask.

You should be asking Straight Talk. Some more information, I don’t know about Straight Talk, but if you‘re thinking about using “AT&T Prepaid service” with the “unlocked” or “SIM Free” iPhone X, watch out, AT&T will lock the iPhone X to their network. Then you will have to follow AT&T procedures to have it “unlocked.”

Some features like visual voicemail, wi-fi calling, hotspot, and others are carrier specific and you need to make sure the carrier supports them on the particular phone you are looking at.

If you bought an unlocked iPhone from Apple, or had the iPhone unlocked by any carrier legally, it will never again lock to any carrier. Its simply not possible.

AT&T cannot unilaterally lock, legally unlocked phones like that, since they would need to go through Apple and the lock database they hold, and Apple would not allow legally locked iPhones to be re-locked.

If the device was bought from places like Best Buy or Target in the U.S. or Carphone Warehouse in the U.K, those places do not sell truly unlocked iPhones. The iPhones can be activated with any local carrier, but will lock to that carrier upon activation.

Legally Unlocked iPhones will never lock to any other carrier again. They will remain unlocked.

I got rid of AT&T because of that threat. I had to unlock my phones, even thought I got them unlocked brand new!