Judging from the link you post, you need to sign up for a monthly program. Do you really want to pay $40 a month or more?

If pay-as-you-go makes more sense, there are other threads you can find using the Search function. One option which comes to mind is to buy a T-Mobile USA PAYG SIM and and $100 credit. The credit lasts for a year and lets you keep your number. After a year, add $10 to retain credit and number AIUI. (Experts please correct.) Other plans are available.

I don't know where you are. If from the UK or other Europe (or experienced there), the US doesn't offer the same range of prepaid PAYG programs you may be familiar with.