[General Questions and Answers] alex_theta:
I bought a ROG Phone 5s and it's not connecting to my carrier here in Japan(KDDI au), although to me it seems like it should be?

Picture:

People always say check frequencies to see if an unlocked phone will work, but they say that as if it's simple and straightforward like buying a PlayStation game for PlayStation or Xbox game for Xbox. Virtually any combinaiton of phone/carrier I look up on various sites invariably gives me the same ratio, where it's like 3/5, 4/5, 7/8, etc supported. I never see any that are 100% supported or even 100% not supported. People say check the frequencies as if it's common knowledge. I don't know what any of these band names/numbers mean, and it's not like you can select it in your phone like a radio. All you can do is mess with the APN.

Last year I bought a One Plus 7T Pro McLaren and regardless of APN settings it didn't show the carrier name on the status bar and just said "No Service." Per someone's advice I bought a prepaid sim card for data off Amazon, one that uses docomo's (another major Japanese carrier) network. Popped that in and it connected immediately without any APN tomfoolery or anything. That led me to believe it would work on docomo's network but not au, so I went and signed a contract with docomo and got a normal sim card. But pop that in and it didn't work. So I gave up and returned the phone.

Now here I am again with a ROG Phone 5s this time, but unlike the OnePlus it actually immediately recognizes the network "KDDI" in the upper right part of the screen and even puts a VolTE symbol up there, which is maybe good sign for calling? The data button at the top changes between reading "4G", "4G+", and "4G++" although I don't know what the pluses mean--I've never seen that before. Considering these things, compared to the OnePlus that just said "no service" it gives me some glimmer of hope that it will work. But despite trying to put in their APN settings it just won't connect to the network.

So that leaves me with several questions.

1. Why does this show the network but the OnePlus did not?

2. Is it actually capable of connecting and I'm just missing a setting or something?

3. If it's not compatible then explain the picture I provided and tell me how I am supposed to anticipate this based on a 3/5 5G and 7/8 4G supported bands list.

4. Why does a prepaid data card on docomo's phone work immediately but a proper sim card from them directly not?

Funny thing is, au even sold ROG Phone 5s at one point and showed it off in stores and ****, so I don't know why they'd do that if it wasn't usable:

ROG Phone 5 ファントムブラック 16GB 通販 | au オンラインショップ | オプション品

スマホ・携帯電話向け「ROG Phone 5 ファントムブラック 16GB」など、オプション品の通販。カバー、イヤホン、充電器など、お気に入りのアイテムを見つけよう。

onlineshop.au.com

IOT完了製品 | au OPEN DEVICE DEVELOPER SITE

open-dev.kddi.com

ASUSの5Gスマホ「ROG Phone 5s・5s Pro」と「Smartphone for Snapdragon Insiders」がKDDIの相互接続性試験（IOT）完了製品に追加 : S-MAX

新スマホ「ASUS ROG Phone 5s・5s Pro」がKDDIのIOT完了製品に追加！ 既報通り、ASUS JAPANが5G対応の最新ゲーミングスマートフォン（スマホ）「ROG Phone 5s（型番：ZS676KS）」および「ROG Phone 5s Pro（型番：ZS676KS）」（ともにASUSTeK Computer製）を日本で2021年11月

s-max.jp

Asus ROG Phone 5S

telektlist.com

auが「ROG Phone 5」を単体販売　SIMロックなしで11万4800円

KDDIと沖縄セルラーが、au公式アクセサリー「au +1 collection」にて、ASUSのゲーミングスマートフォン「ROG Phone 5」を5月28日に発売する。auオンラインショップとKDDI、沖縄セルラー直営店で取り扱う。メモリが16GBのモデルとなり、価格は11万4800円（税込み）。

www.itmedia.co.jp