The phone is A1387.
That's
not an iPhone 4 then, it is a
4S. The 4S is actually a totally different beast.
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The 4 is known internally as phone version 3.1
The 4S is known internally as phone version 4.1
I have one of those A1387 models here also, but it is in pieces, with multiple hacks and power wires soldered onto it to make it run just enough to get the person's photos, etc. back, so that's no help.
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The phone reports iOS 9.3.6 and "Up to date"
When I try to download Wechat it says "not compatible with this phone".
Yeah, for the 4S, you can still either run 6.1.3 or 9.3.5/6, so yours IS actually up to date, on the 9 branch. (It COULD also say it was up to date on the 6 branch, depending on what OTA update stream your carrier was sending you.)
According to wechat's system requirements, the latest version requires iOS 9, which you have,
BUT for whatever reason, the 4S is now explicitly excluded from their supported hardware, even though it runs 9.x....
Requires iOS 9.0 or later. Compatible with iPhone 5S, iPhone 6, iPhone 6 Plus, iPhone 6S, iPhone 6S Plus, iPhone SE, iPhone 7, iPhone 7 Plus, iPhone 8, iPhone 8 Plus, iPhone X, iPhone XS, iPhone XS Max, iPhone XR, iPhone 11, iPhone 11 Pro, iPhone 11 Pro Max, iPad Air, iPad Air Wi-Fi + Cellular, iPad mini 2, iPad mini 2 Wi-Fi + Cellular, iPad Air 2, iPad Air 2 Wi-Fi + Cellular, iPad mini 3, iPad mini 3 Wi-Fi + Cellular, iPad mini 4, iPad mini 4 Wi-Fi + Cellular, iPad Pro (12.9-inch), iPad Pro (12.9-inch) Wi‑Fi + Cellular, iPad Pro 9.7-inch, iPad Pro 9.7-inch Wi‑Fi + Cellular, iPad Wi-Fi (5th generation), iPad (5th generation) Wi‑Fi + Cellular, iPad Pro 12.9-inch (2nd generation), iPad Pro 12.9‑inch (2nd generation) Wi‑Fi + Cellular, iPad Pro 10.5-inch, iPad Pro 10.5-inch Wi‑Fi + Cellular, iPad (6th generation), iPad Wi-Fi + Cellular (6th generation), iPad Pro (11-inch), iPad Pro (11-inch) Wi-Fi + Cellular, iPad Pro (12.9-inch) (3rd generation), iPad Pro (12.9-inch) (3rd generation) Wi‑Fi + Cellular, iPad mini (5th generation), iPad mini (5th generation) Wi-Fi + Cellular, iPad Air (3rd generation), iPad Air (3rd generation) Wi-Fi + Cellular, iPad (7th generation), iPad (7th generation) Wi-Fi + Cellular, iPod touch (6th generation) and iPod touch (7th generation).
Notice the conspicuous absence of the 4S, even though it is the earliest phone that will run 9, so it looks like you're SOL for that app on there for some unknown reason, unfortunately. Who knows why they blacklisted it from their app. It probably doesn't support some tracking feature.
I think at this point I just give up and switch to the Samsung Android because 3G is being shut down and the iPhone 4 will no longer work with data. I wish I could find some use for the iPhone rather than putting it away in a box.
It would just fall back to 2G/EDGE if they do totally shut off your 3G. I don't think 2G will be going anywhere for a long time because there are too many embedded devices that use it, at least around here there are, anyway. Everything from cars to home alarm systems. The A1387 supports 850, 900, 1800, 1900 MHz 2G/EDGE. Actually, the 4S is one of the few iPhone models that (as far as I know) was only made in a "world" variant, except perhaps some Chinese-market-only variant. I believe they usually all support both CDMA
AND GSM, in the following bands:
UMTS/HSDPA/HSUPA (3G) @ 850, 900, 1900, 2100 MHz
GSM/EDGE (2G) @ 850, 900, 1800, 1900 MHz
CDMA EV-DO A @ 800, 1900 MHz
That actually makes it one of the most system-compatible phones unless you are in some area that turns off everything except 4G/5G, but that would leave a lot of stuff other than phone handsets unable to connect to anything.
You can always use an old phone via wi-fi only, like a mini-mini-iPad of course, but when you lose access to the only apps that you care to run (like wechat in your case) it becomes somewhat pointless. If I need a small portable device at some site for something, I grab an appropriate phone from my stash and use it for whatever I need, on the local wi-fi... They do make nice little "iPod" devices, or remote controls with the appropriate app or some customized website access or whatnot.
I would never stick my SIM card in one of those dirty things, though.
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