Absent a formal policy, is it rude to use a mobile phone to take notes in lectures and seminars?
Phones are not perceived as note-taking tools, making them undesirable in education and business settings. Laptops are tolerated in both settings, but don't expect respect. Tablets are perhaps the lesser-evil, especially when used with a stylus. Better still, specialised note-taking devices (not dissimilar to tablets) are now available. Paper will serve you well and set the best impression.