First off, Solavei sells an actual product that works as intended (T-mobile MVNO). You don't pay the referrer anything, nor do you have to provide seed money that isn't normally required for cell phone service (i.e. activation cost, sim card purchase, service cost). Also, you pay your subscription fee to the company itself, not a referrer and can cancel the service at any point. If it is a pyramid scheme then I must not understand exactly what differentiates a real business with tiered referral bonuses from a scam (feel free to drop knowledge on me about it, I'd love to know).
Second, you don't have to join their whole referral program thing to sign up for cell service. Neither my wife nor I are part of it. We just pay each month for cell service.
Finally, even if it turns out to be a pyramid scheme it won't just get shut off over night. Even if you have short notice, though, since it is prepaid you can just hope to another provider without any trouble.