As soon as you start downloading, if you abuse or somehow download too much, they will downgrade your account. Also you should check if unlimited download will be at the same 256kbps speed or 64-128kbps.
However, Fair Usage Policy is usually flexible, and it can be changed depending on several factors.. like number of subscribers and load. Most of the ISPs change usually their FUP during time.
Believe me there is no such unlimited downloads and quota in Lebanon
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