You may get some
sales even with a weak or nonexistent call to action. But you'll almost certainly get more with a strong, obvious, visible CTA.
Of course, you don't need any kind of email or online promotion service to create a strong CTA. All you need is a big ol' highly-visible "BUY NOW" button on your product page, or a giant, brightly-colored "SUBSCRIBE NOW" button on your newsletter sign up page, or a prominently-placed, large-font, bold-faced "REQUEST INFO" link on your lead generation email.
The point is, you don't need anybody's "service" to include a CTA. All you need to do is not be shy
about telling people what it is you most want them to do when they land on your page or read your email or view your ad.