Your friends were probably excited because they didnt have a character limit when sending a text, they didn't have to pay for each message they sent, they could share images, videos. All of that for the fraction of the cost of sending a text message.
I would even include the better interface, as it had a better look than the regular SMS screen. Character limit wasn't the deal because their whatsapp message are still short. And even the cost of messages was negligible, because the main point of the cell phone plans were unlimited messages.
And photos and videos were available as email, skype, messeger...
I would bet that here (in my country), SMS wasn't sexy because of the interface, email wasn't that real-time conversation (and you needed to know the e-mail address).
Needing just the phone number (that was a common thing to share), not using e-mails (that was seen as too tech, too formal) and having a better look than the SMS interface was the point. All other features were just a bonus.
