In days of old when knights were bold, yada, yada, yada, the Coast Guard would tow your boat if you simply broke down. Those days died during the Ronald Reagan administration, when the cost of nautical charts skyrocketed and the Coast Guard had to change its policy, among other things, in favor of private towing companies. If the Coast Guard does give you a tow, it will be to the closest marina or place you can tie up, not necessarily back to your dock or where you launched your boat.
Today, unless there is an imminent threat to life, if you call the Coast Guard you will likely be told to call a commercial towing company. Among the more prevalent are Towboat US (a BoatUS company) and SeaTow. Often both companies will be operating in the same area, and there may be others as well.
The problem is that you do NOT want to need a tow (or fuel, etc.) and not have insurance. The cost of one or more tow(s) is very high! This should be a strong motivator to carry insurance that covers the cost of a tow, similar to having AAA or similar for your vehicle tows or breakdowns. Do not get caught needing a tow when you left your wallet at home on the dresser!
Both TowBoat US and SeaTow offer a variety of membership plans that provide towing insurance for you, if and when you need it. Both companies have a phone app that, among other things, has a button to click so they can send a tow based on the GPS position on your phone. Other companies may be out there and offer the same things, -so we are not recommending any particular service. We strongly recommend that you do have insurance if you go out on the water in an area where one of the services is available. Be sure to check availability in your area before committing to a membership.