Imense amounts of insurance, usually at least 5 million. A huge performance bond. You have to guarantee the work your subs do for up to 5 years (Verizon of California). And you have to be able to come up with a substantial work force at the drop of a hat. It is a large undertaking.
This is CABL.com posting #146610. Tiny Link: cabl.co/mMiQ