Does Gear S2 send and receieve off IMEI or SIM when using AT&T Numbersync?

[CrazyCamel369#AC]

Pretty much what the title is asking. I have a Nexus 6P but had to switch my IMEI on AT&T's system to show a Samsung S6 to have my Gear S2 work with Numbersync, I'm just not sure if my friend will receive my messages or not because I'm using his IMEI.