Don't know if it is still the case, but for $25 one time fee (much less than one month of average phone bill) you could port your number into Google Voice, and

Don't know if it is still the case, but for $25 one time fee (much less than one month of average phone bill) you could port your number into Google Voice, and keep it forever, at least until Google shutters Google Voice (which they likely won't, because it's such an incredible spying device).