Continuity of Messages
Thanks to the Messages app, you can talk to pretty much any one of your contacts in a matter of seconds, but that’s just the tip of the iceberg.
With iMessage, you can pick up a conversation you had years ago, and your iPhone will still remember what the last message you sent was. You’ll have this continuity even if you’ve switched iPhones recently. Now compare that to the limited number of messages you could have in the first telephone, and you’ll be amazed.