The devices, manufactured by Elster, are designed to help companies monitor and reduce energy costs.
Livingston-based Energy Assets said its 20-year deal, which allows for annual inflation-linked price adjustments, will boost the growth prospects from its long-term recurring revenue portfolio.
It builds on the role Energy Assets has already played in delivering the advanced meter strategy of British Gas Business (BGB).
Working with Elster, it has helped develop a new meter that allows for the remote communication of consumption data. That product is the primary technology which will be rolled out to BGB's I&C customers.
While precise information on the size of the BGB portfolio is unavailable because of customer confidentiality, Energy Assets' house broker Numis Securities estimates that it stands at between 100,000 and 120,000 meters.
Numis updated its recommendation on Energy Assets shares from buy to add, and increased its target price to 530p from 380p. Phil Bellamy-Lee, chief executive of Energy Assets, said: "This is a significant step in the achievement of the Energy Assets growth strategy and is testament to the relationships we have developed with BGB and Elster."
Shares in Energy Assets closed up 32.5p at 390p.
Glasgow-based SMS said it will replace BGB's existing diaphragm and pulse output meters with Elster meters, which have an integrated data communications system. It expects the roll-out to be complete by 2017.
Chief executive Alan Foy said: "We are delighted that BGB has chosen SMS to undertake this meter-exchange programme over the next three years.
"The signing of this contract is another step towards our ambition to become market leader in the independent ownership of I&C meters and in the provision of automated meter reading solutions for our customers."
Matt Idle, of British Gas, said the Elster meters "will enable our corporate customers to benefit from innovative technology, which will make it easier for them to control and reduce their energy costs".
Shares in SMS closed up 5p at 390p.