Experiencing Issues with iMessage and SMS on Apple Watch Series 7 GPS

The Apple Watch GPS model is physically incapable of sending SMS. It can ONLY send SMS by relaying through the iPhone’s cellular radio.

If you basically disable the iPhone’s ability to send SMS, and access the internet, the Apple Watch still has WiFi and can send iMessage to the users if the user is capable of receiving iMessage messages.

NOTE: Even a cellular Apple Watch has to relay SMS via the iPhone, as the Apple Watch cellular radio is data only, and performs phone calls using VoIP (Voice over IP), which does not support the special signaling needed for SMS.

If you wish to send SMS, then the iPhone must be powered on, it must be connected to the internet, and it must be signed into iMessage (which relays the SMS request to the iPhone). The Apple watch must be signed into iMessage, and be able to talk to the iPhone via either Bluetooth, WiFi internet access, or cellular internet access.

The Apple Watch CANNOT send SMS. It does not have the hardware to do that. ONLY the iPhone can send SMS on behalf of the Apple Watch. So it is impossible to keep the iPhone out of the SMS loop.

Get your iPhone to do what you desire, and do not cut communications between your iPhone and your Apple Watch, stay logged into iMessage, and do not turn off the iPhone’s cellular access. Then, the Apple Watch should send SMS.

If iMessage is disabled on the connected iPhone, the watch sends the message to the connected iPhone, which then sends the text as SMS.

If the iPhone is not available, the watch can not check the settings for messages before.

In that case you would need a cellular watch, which can determine the availability status before sending the text message.

The Apple Watch does not know, that iMessage is not available at this time, because the iPhone is switched off or can't be reached, containing this information.

So the Apple Watch uses the iMessage, since the recipient has used iMessage previously.

Only the iPhone can send SMS directly, the watch only sends the text message to the iPhone, which sends it in the end, depending on the availability of the service.

Without the iPhone connected to Wi-Fi and your Apple Watch, you can not send/receive SMS.

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2. To receive SMS, MMS, or push notifications from third-party apps on your cellular Apple Watch, your paired iPhone must be powered on and connected to Wi-Fi or cellular, but it doesn't need to be nearby. You also need to be signed in to iMessage on your iPhone to use Messages on your watch.

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copied from: Use your Apple Watch without your iPhone nearby - Apple Support

If my watch is connected to my iPhone and I want to send a text message to a known Android phone number, I have to choose the phone number from my contacts, then fill in the text, and the "Send" button is green.

In case of a known iPhone number or Apple ID, the message in the text field says "iMesssage" before I type the message into that and send it.

The Apple Watch is choosing SMS or iMessage according to the contact info saved in the contact app.

What happens, if you type in the Android phone number manually on your Apple Watch, before sending the text message as SMS?

As mentioned, the Apple Watch can not decide itself wether to use SMS or iMessage. Unless you have the Cellular model, your connected iPhone decides how to send the message it received from your Apple Watch, in order to send it to your recipient's contact number.

SMS is a carrier based service and as long as your Apple Watch has not cellular connection without the iPhone, it sends text messages as iMessages, which are the default settings for a non cellular model and an iPhone being out of reach.

If your Apple Watch has no cellular option, you can only send & receive text messages (SMS) if your watch is connected to your iPhone via Wi-Fi or Bluetooth.