Vegas does the same thing. My email is normally set up to go on, send & retrieve messages & then disconnect, but of course after reading messages offline, I'd have to go on again to send, etc, and incur additional charges.
So what I do is go online & stay online & disconnect at 59 minutes. If I need to go online later, I do the same thing. Significantly reduced my hotel phone bill.
You could be in worse situation - in London they charge by the local unit & my hotel phone bill was $150 in one week at the Langham Hilton.
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Sharon