Can I park my number with String?

In this article:

Perhaps you just want to hang on to your String number but aren't ready to use it quite yet. Or you aren't using your plan but plan to in a month or so.

Instead of canceling your service, you can choose to have String hold your inbox indefinitely for $1.99 per month. This will preserve your conversation history, retain your phone number, continue to receive incoming messages, and allow you to reactivate your account at any time.

To have String hold your inbox, follow the process in this article:

How do I cancel my account?

Be sure to push the Hold my inbox ($1.99/month) button.