M. -
I don't know where all the locations are, but my son goes to Children's Choice Learning Center - there are several all over the Metroplex. They are 24 hours a day, have sick rooms (meaning if your child is sick, he/she can stay there and be tended by a nurse), and take drop-ins. I first found them because I needed back up daycare, too. Eventually, they became my permanent (my nanny went back to school). I really like the company - good philosophies, great atmosphere, and we use them for date nights, too.
Not sure if there is one in Frisco, or maybe close to wherever you work, but worth checking out. Their website isn't that thrilling, but will give you some basic info. www.childrenschoice.com. Most daycare centers that I know of allow drop-in care. You usually just have to pay a registration fee. I can't vouch for others, but I can say that there was only one time the Children's Choice couldn't accomodate me. Think the 24 hour thing gives them some more flexibility than other centers. Good part about that is you can call late at night to ask about the next day because someone will be there!
Congrats on your upcoming journey into parenthood! And good luck with daycare - it can be a stressful decision-making period.
S.