Listen, the cell phone is a bit of a 'red herring' in this whole saga. Fact of the matter is that every now and then a set of circumstances present themselves that lead to a crew becoming distracted and forgetting to carry out normal actions. I seem to remember a story in the press from a couple of years ago regarding a Qantas 767? that ended up doing a missed approach in Sydney because they 'forgot' to put the gear down and got the 'to low gear' warning. Most of these incidents are caused pure and simply by distraction. We are trained to do things in a certain order and at a certain time and it CAN only take a minor distraction at an inappropriate time to get yourself totally out of whack. In this case it was the Captain's attention being taken away doing whatever he was doing with his phone, this led the First Officer to become distracted as well.
I have done it myself once, but not to this degree. We were on a complicated visual manourvre to a very scenic runway surrounded by terrain in Europe. We had always been taught that at 2000' you took Flap 2, Gear Down, Landing checklist. On this particular day I was flying and at 2000' I asked for Flap 2 and at that point the Captain pointed out a very impressive looking house on the side of the hill, it drew our attention outside the flight deck for a couple of seconds but it was enough to interrupt the normal flow. At around 1700' whilst trying to slow up to get Flap 3 out I commented that it was taking longer than normal to slow up, I had that feeling that something was not right and started going through my normal flow of 'right, we have flap, we have gear........ **** no gear!!!' Thankfully it was caught really early, but to this day I still remember it as an example of how quickly things can get out of shape.
In the Jetstar case these two crew had hardly said a word to each other for hours and were NOT providing good support for each other. The phone provided the initial distraction, then the go around altitude provided further distraction. I am sure they got the 'something is wrong' feeling. The biggest worry in this situation is how long it took them just to throw it all away and go around once the too low gear warning went off.
It is quite common for retractable undercarriage aircraft to be landed without the wheels, normally caused by the pilot having been distracted. No one sets out to make these mistakes, but they will ALWAY's happen, it is more important to react appropriately to the mistake, trying to push on and make the landing anyway is not the right response.