Transport for London has issued tenders for two contracts with a potential combined value of £150m.
The first seeks suppliers to "ensure successful transition of services from project to network support". It wants providers which have "successfully delivered relevant large transformational programmes".
The estimated cost is between £40m and £75m.
Under the second contract, TfL wants a supplier to "manage, support, develop and rationalise its voice and data networks".
The company wants "a cost-effective infrastructure to support all aspects of its voice and data requirements" and the contract will include network management.
The contract is worth between £30m and £75m.
Both contracts are expected to be awarded in November 2010.