Isn't the Athaan a type of alarm anyway? Come on, I think this may be a little extreme. I get the point that it is disrespectful because you are stopping the recitation to answer the phone, but this is not the intention to be disrespectful. Everyday we hear the Athaan and stop what we are doing to pray, this is a type of alarm. I think having the Athaan on your phone to remind you to pray is good, but maybe not for an alarm. Maybe it would be better all round to use some type of dua or nasheed. This is all just my opinion. I think the majority of the time we are being tested on our intentions. Everything has to do with the intention.