To Tweet or Not to Tweet

It has been our assignment in PIDP 3240 to get to know Twitter.  After having it installed on my phone and testing it for the last 6 weeks, I came to the conclusion that Twitter may not be the best way to stay in touch with the students.  The reasons for being disappointed in Twitter are as follows:

1. Timeline is hard to follow
2. Ads
3. People can re-tweet stuff I am not interested in

In the last couple of days, I looked into alternatives to Twitter and came up with two text messaging services:  ICQ and WhatsApp

Any suggestions on either one?

What are your thoughts regarding keeping discussions closed among a learning community versus opening up to a wider, public community?