Siri is great for sending, receiving and replying to text messages using the Messages app. This works fine for sending messages to both iPhones and Android phones. Siri can't do everything you might want to do with messages, so you may also need to learn how to work with messages using the Messages app as well as relying on Siri. Siri works best for people with sight loss if VoiceOver is switched on and these instructions assume that VoiceOver is turned on which causes Siri to be more talkative.
To send a text message, instruct Siri to "text John Smith" or "message John Smith" and you will be asked to dictate the message. When you stop speaking, Siri will speak your message to you and then ask if you are ready to send the message. At this point you can say "yes" to send the message or, alternatively, one of "cancel", "change" or "read". "Change" allows you to replace the message. "Read" will speak the message back to you again for checking. "Cancel" abandons the message.
Siri can usually handle the names of all your contacts but occasionally seems to get confused. If you have problems with this try spelling either the first or last name of your contact in your request to Siri. For example, if Siri has problems understanding you when you ask it to text Balwant, try saying "text B A L W A N T" instead. This usually works and often restores Siri's ability to recognise Balwant's name.
When your phone receives a text message, you can have it spoken by instructing Siri to "read messages". This will read all the messages that you haven't read yet, one by one, and at the end of each message, you will be asked if you want to send a reply. You can say "yes", "no" or also "read" if you didn't catch the message first time.
Once Siri has read a message and moved on it can no longer be read by instructing Siri to "read messages". If you instruct Siri to "read messages" again you will be told that you have no messages, which actually means that you have no unread messages. If you need to hear a message again later, then you must either use the Messages app or ask Siri to read a specific message or messages, for example "read my message from John Smith" or "read my messages from yesterday". The results can be a little erratic but are often useful.
So long as WhatsApp is set up on your iPhone Siri can normally deal with WhatsApp chats similarly to the way it handles text messages using the Messages app. Saying something like "text Jane Smith using WhatsApp" and "read my WhatsApp messages" should work. "read my WhatsApp message from John Smith" seems to behave erratically. If you tend to use WhatsApp to communicate with an individual, Siri may remember that and use WhatsApp if you simply ask for a text to be sent. At other times, Siri may ask you to confirm whether you want to use Messages or WhatsApp. Occasionally those requests aren't handled correctly with spoken prompts for VoiceOver users in iOS 18 and I'll be checking the iOS 18.1 release soon but it isn't always easy to persuade Siri to ask the question about which app to use!.
iOS 18 is starting to roll out Apple Intelligence to selected recent devices starting with US English in iOS 18.1 to be launched on October 28 2024 and adding further languages later in 2024. If Apple Intelligence is supported on your device and language Siri may initially give summaries of messages and ask if you would like to hear the full message. The setting for Messages summaries is at Settings / Apps / Messages / Summarise Messages. For WhatsApp, the setting is at Settings / Notifications / WhatsApp / Summarise Previews. I have n't yet checked how the WhatsApp setting interacts with Siri. All of this is only relevant if Apple Intelligence is supported on your device and language and that probably won't include UK English until December.