I'm a call center agent. When I ask to transfer the call to the authorized person, which form should I use:
Can I speak to...?
Could I speak to...?
Only pedants or jokers would reject "Can I speak to..." or "Could I speak to...", any of these are acceptable, especially if you include the magic word ("Please").
While some people may find it overly formal, I would think "May I please speak to..." should be almost universally acceptable.
P.S. I remember a certain older gentleman who took great delight in torturing my young self with exchanges such as this:
Me: "Can I have a cookie?" Him: "Yes, you can, ..." (but doesn't get the cookie jar) Me: "... Could I have a cookie, then?" Him: "Yes, you could, ..." (still, no action) Me: "May I have a cookie, please?" Him: "Yes, you may." (finally, I get my cookie) :)