I’m pretty sure I just sent my cellphone number to a Craigslist scammer. What’s the worse they could do with my number?

It depends how sophisticated they are. If they knew what service you were on, they might be able to socially engineer access to your account, but that is no doubt a distant possibility.

If all you gave them was your phone number, I think you’re ok. If you have credit/debit cards, check your account activity closely.

You might try contacting your service provider and make the aware of the situation. They may have some protocol that would protect you.

They can send you fun wallpapers and ringtones and smileyfaces!
More of a blessing than a curse.

Call you at all hours of the day and night.

The worst thing I can think of is they can sell your number (and many others’) to a bunch of advertisers.

If it’s the same number that starts calling you, it’s possible to block it. Call up your provider.