In that case it would work. I was under the impression that you'd be syncing with everyone so someone in New Zealand could contact someone in Canada.

The average person has 208 twitter followers. So lets say you have 208 'friends' + a couple additional 'friends' for each of your original friends. That's 624 people total.

There are 100 million active twitter users each day and 500 million tweets per day, that's 5 tweets per person.

5 * 624 = 3120

That's 3120 posts you'll be processing per day. Multiply this by 140 bytes per post and you have 436800 bytes per day or 159.5 MB per year.

That's manageable.