Apple watch

I was wondering if the Apple Watch that I bought is unlocked. I have AT&T and I bought the watch form the Apple store and it is GPS and Cellular. My daughter wants to use it as her phone while she is in school and I hoping I didn’t buy the wrong one. It doesn’t say anything about a certain service provider but it also doesn’t say it’s unlocked either. I haven’t opened it yet because her birthday isn’t until Aug. 2nd but I’m sure it won’t tell me anything more than what the site I bought it from tells me. Please help.