1&1 AG shares surged after it secured a deal with Vodafone Group Plc that will let the mobile provider resell 5G service in Germany. Telefonica Deutschland Holding AG, which has the current contract to provide mobile network access to 1&1, sank the most ever in Frankfurt trading.

Vodafone’s German unit and 1&1 have committed to an exclusive agreement for five years beginning on Oct. 1, 2024 at the latest, the companies said in a statement on Wednesday. The deal includes options to extend for another 13 years, including a transition period. 1&1 will pay a fixed price based on the percentage of Vodafone’s network that its customers use, the companies said without disclosing any more financial details.

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Telefonica Deutschland issued a separate statement confirming its 2023 outlook and dividend commitment. The company also said that its existing contract with 1&1, to provide 4G service, goes until June 2025.

1&1 — which was launched as a “mobile virtual network operator,” reselling service from other carriers — is preparing to start selling service under its own network at the end of next month. The carrier will be able to use the agreement with Vodafone as a “significant buffer, providing access to a high-quality 5G network while any issues are addressed” with the rollout, Bloomberg Intelligence analyst Erhan Gurses said.

Customers with 4G mobile tariffs will keep access to roaming from Telefonica Deutschland for now. 1&1 will provide 5G coverage under its previous MVNO model, using services from Telefonica or Vodafone in the interim.

1&1 shares surged 15% to €11.80 at 3:06 p.m. in Frankfurt trading after earlier gaining as much as 17%, the biggest intraday gain since 2011. Telefonica Deutschland fell 15% after earlier dropping as much as 18%, the most on record.