to keep on eye on: estar pendiente de.
On the one band....On the other hand
Nowadays most people have a movile phone, although we use it to make phone calls, we prefer to communicate with our friends and family by text messages
On the one hand text messaging is a fast way of communication, It is cheap or even freen. Besides, You can use it everywhere, anytime
On the other hand we are always keeping and eye on our phone, every day we have lets of messages to read. We have to read them all although we are not interested in many of them.
Persoanally/in conclusion I think that text messaging is very useful but I don't use it too much. I prefer face yo face comunication