I've recently opened an online savings account with the NatWest, who have been my Bank for donkey's years. They left a telephone message asking me to contact them as they needed more information before they could open the account. Called in at the Branch, who checked and said all they need is my telephone number. I gave it to her and the account was opened. It was only afterwards it occurred to me that if they didn't know my telephone number, how did they ring me in the first place?!
I had to call a company recently with a query, and as it was not quite straightforward I needed an English speaker, so I asked the person who eventually answered [after the performance of the menu] if she spoke English. The answer, in English, was no, give me your number and someone will call you back. Someone actually did call back - I explained the query and he said he would look into it and call me again. He then asked for my telephone number - but he had only just called me on it!