Does At&T International Pass work in Tibet?

i'll be traveling on a tour in tibet for 16 days. i have AT&T and they say that i can access service via the international day pass in tibet. has anyone used it there? is coverage good? i will want to use my phone to check my email, banking app, instagram, alipay & wechat. the other option is paying off my iphone installment loan to unlock my iphone & use an e-sim card