Remind me when messaging is an interesting feature of the iPhone Reminders app and it can be very useful. Never forget tasks and things to do when messaging people by creating a reminder.
Things you need to do and don’t want to forget should be added to the Reminders app on the iPhone. Reminders can be anything from shopping lists to work projects and can contain anything you need to remember to do.
Reminders can have triggers that cause them to be automatically displayed on the screen, rather than you having to open the app and look for them. For example, you might want to be reminded about something at a particular time on a specific day. Reminders can be triggered by the location too, and you could set one so that tasks appear when you arrive at work or at home. You could even have your shopping list automatically appear as you arrive at the supermarket.
Another trigger is when messaging someone. You might want to be reminded about something when chatting to them using the Messages app on your iPhone. For example, you might need to send someone some information or an image, you might want to be reminded to ask how a project is going, how a mutual friend or their partner is doing, offer help with something and so on.
The Remind me when messaging trigger can do that. The reminder appears immediately after you have sent a text message.
After selecting the person to text, it would be more useful to show the reminder then, but it is still useful to see it after sending a message. You can always follow up a message with “Oh, by the way, here is that info you wanted.”
Here is an easy-to-follow step-by-step guide.
1 Open iPhone Reminders

Open the Reminders app on the iPhone and then open the Today list. Down at the bottom of the screen, Tap New Reminder.
2 Create a new reminder

Create the reminder you want to see when you message a certain person or company. The content is up to you and it can be short or long and contain any information you need. Press the i button on the right of the reminder.
3 Customize the reminder details

There are the usual options to set a date and a time to be reminded, and the location reminder, but right at the bottom is the option we need – Remind me when messaging. Turn it on.
4 Choose a person

When this option is enabled by turning on the switch, a Choose Person link appears below it. Tap it to continue.
5 Select a contact

The Contacts app appears and you can scroll through the people and companies and select one. Tap a contact to add them to Reminders.
6 Check and edit

You can now see in the reminder Details screen who this reminder applies to. There is also an Edit link which enables you to change the person. Tap Done at the top of the screen to finish.
7 View the reminder

This is what the reminder looks like. There is the reminder text and below it is the trigger that causes it to be displayed on the screen. You can see the person that will trigger the reminder.
8 Create a new message

Open the Messages app and add a contact in the To box at the top. This is actually when I would like to see the reminder appear, but it doesn’t. You have to type a message and press the send button.
It can be an iMessage or a plain text message, it does not matter. The trigger is the person you are messaging.
9 See the reminder

As soon as you press the send button, the reminder pops up at the top of the screen. It lets you know if you have forgotten to include something in the message or if you need to send another message with the information the person needs and so on .
It probably isn’t a feature that will be used a lot, because if someone needs something, I usually send it straight away or set a reminder to send it today, tomorrow or when it is due. However, it is useful to have extra options available to you.