What is the ruling on swearing not to use a mobile phone when angry, knowing that there is a need to use it, and does this entail expiation?

An oath sworn in a state of anger is binding, and it is not permissible to supplicate for one's own death. If the intention of the oath was to supplicate for one's own death, then there is no expiation (kaffarah) required, and only repentance is necessary. However, if the intention was to refrain from making calls, then it is an oath, and it is legislated to offer expiation for it if the questioner wishes to make permissible calls.