The Electric Reliability Council of Texas (ERCOT) does it for you. When you sign up for a plan with a new provider, ERCOT will send you a mailer confirming the switch. You have three days upon receiving the mailer to change your mind. If you don't, you'll have a new provider within seven days, and ERCOT will notify your old provider. Just remember, if you abandon a contract before it's complete, you will be on the hook for any fees or penalties detailed in its Terms of Service.
Then, in 2002, Texas deregulated the electricity market and everybody cheered! Except that, sure, deregulation opened up the market to competition that may (or may not) have resulted in lower rates, but it introduced a whole host of other issues. These issues may not have been factors before but now they’re critical when you’re on the look-out for cheap Houston electricity providers.