To send to a contact's specific #, there should be a disclosure arrow to the right of their name (as you're entering it) you can tap and then pick which # you want. You can also double-tap a name in the To field.

There’s no visual indication of which number messages are going to and arriving from for an existing conversation, though. Messages to and from all numbers are just collapsed into one thread.

It gets even worse when iMessage and multiple devices come into the mix. It all kind of works for 95% of people I’m sure, but it completely falls apart in some cases with absolutely no way to be more explicit.

Totally agree. I was on Google Voice till earlier this year and that was its own kind of awful. After more than a decade on GV, I ported my number back to my carrier. I keep WhatsApp on my phone to use with a single family member on an Android phone. Another member with an Android phone uses whatever the built-in messages app is. Everyone else is on an iPhone. It's a mess.

The annoying part is, that this ends up going back to the lowest common denominator. Where users that wont install another program end up being the boat anchor dragging everyone else to the bottom.

> most frustratingly I can’t send an SMS to any contact it believes to be on iMessage

You can long press on a sent iMessage blue bubble to reveal a 'Send as Text Message' menu item. It's quite hidden but it's there.

Only if the message didn’t go out to Apple’s servers. That doesn’t help me when I know the recipient won’t be able to receive it (e.g. because they are on roaming or out of mobile data).

If you know you want to send an SMS you can tap it right after you press send, there’s a small grace period. I just did it.

You can long press on the message bubble after hitting the send button in Messages to switch between sending as iMessage or SMS. Discoverability of UI/UX features on both iOS and Android is inscrutably horrible.

That button only appears when I don’t have a data connection.

Potential workflow, not that I consider this “sane” but rather a workaround:

Swipe up from bottom screen edge to open Control Center, toggle Cellular Data off, send as SMS, then toggle Cellular Data back on?

The ol' three-swipe-salute as it's known in some parts.

Maybe asking siri for help on this is the apple way.

What happens if you specifically ask Siri to send as text message and NOT iMessage?

I can choose what number I want to send from when using two SIMs. It's shown as "From" below the "To" when you write a new SMS using the new message button. In an existing conversation you need to tap on the contact icon and change the "conversation line" there.

delivery receipts = read receipts? They are a setting.

Tap on their name to change the "to" address; here it gives me a list of their Apple ID email and phone number to pick from.

You can enable fall-back for contacts which fail to send via iMessage to instead send via SMS, but I don't think you can send SMS to a phone number registered with iMessage by default without disabling iMessage globally.