When a prior user of this number did not receive a fax from a unique (different from the number from which you previously received a fax) every 7 days, it gets put into a pool of available numbers for a period of time. After a while it gets assigned to a new free user. If the prior user decides to upgrade to the paid service and wants that number back, they will get it. Basically, when a number is in demand, the first person to pay for it gets it.
If you do decided to keep your current fax number and upgrade to a paid account, we will give you a free month for your inconvenience. Simple mention this email after you upgrade and we will add the free month to your account.