Maybe it's just my crazy Irish mindset, but to me someone's intentions play a significant part in the whole politness thing. It's like if you're having a conversation with someone, and another person marches up and interrupts the two of you. You can chose to ignore him and carry on, that doesn't make his interruption any less rude. Same idea with texts messanges vs. calling someone.
But in the end, different parts of the world have different rules of etiquette, and the rules I'm used to say that calling someone is a bit rude, and rather presumptuous but it seems you zany colonials have different ideas on the matter.
