There was a time when you sent your last T9 text message and you didn't even know it was the last one. Remember? You had to type letters out by hitting the number keys a certain amount of times? It was tedious, but in it's day, it was kind of miraculous.
Or the time you logged onto AOL Instant Messenger for the very last time. Remember that door squeaking open sound when someone you knew came online? That ding when they messaged you? Yep, you logged off one day and you never realized you wouldn't be back.
There are a bunch more in this article and the last one is really the most touching because at some point in your childhood, you did this and didn't realize it would be the last time.