I cite the sources further down in response to a sibling comment. You're right, I didn't amortize the interest: fixing that brings the pay-off period to a bit under 25 years, not 37.
https://www.cga.ct.gov/2012/rpt/2012-R-0515.htm
At 4% interest, 83 000 subscribers and attributing none of the costs of the fiber network to the smart meter project the payback period is 10 years and 7 months. A far attribution of costs to the smart meter project would bring the payback period to under 10 years.