Badly designed product
Before I begin, I'd clarify what is meant by 'bad'. I'm assuming that I can suggest improvements to a product I use today. When I think about products I love using today, I have a simple criteria:
1) Product solves a need that no other products solve the same way, it's unique
2) I use it frequently use it and it works
3) The product is intuitive
The product I will focus on is iMessage (iPhone native messaging app). I've come to use other messaging apps more because they have unique characteristics that I think iMessage is missing.
The user cases for iMessage are:
1) Sending a message to someone from your contacts
2) Searching messages for something previously sent
3) Searching someones contact info from your list of messages
4) Sending a photo to someone
5) Calling someone from your messages
6) Searching for photos previously sent
7) Replying to texts recieved
When it comes to iMessage, iPhone can do 1, 4, and 7 with the least amount of clicks. However, I think the rest of the tasks can be improved. I think when it comes to user efficiencies, you want to be able to achieve a task with a minimal amount of clicks. User cases 3 and 5 take more than 1 click. Where as on other messaging apps such as WhatsApp it is easy and more intuitive. Finding contact info should be super quick. In iMessages it takes 4 clicks to find out what the users phone number is. That isn't intuitive.
Search doesn't exist for 1:1 mesages on iMessage. I find that saving a message to come back to later is hard. For example, a user scenario could be saving someone address info or apartment buzzer. Currently, right now you search for all your messages and the app will return messages from all your chats even if you know who you want to search messages with. The improvement I would suggest here woud be - being able to save messages and come back to them later.
Another improvement for #7 is to be able to reply to older messages. Scenario here would be if you were having a group conversation and weren't active in the conversation at the time. When you go open up your messages, you can go through the conversation and reply back to messages you might have missed. Currently, you reply is general to the conversation and not specific to someones message. WhatsApp has also solved this problem well.
To summarize, more users will resort to using other messaging apps since iMessage is lacking intuitivity.