I don't think Amp'd counts as a competitor to loopt. Amp'd is an MNVO that's doing a lot more than just providing a single mobile phone technology. Burning through that sort of money is relatively easy when you're paying through the nose to be on someone else's network and you're doing national advertisement campaigns.
As Techcrunch notes, it "probably sits more as a telco failure than a strict Web 2.0 one"