In general, Telestial is a trusted, up-front company with good customer
service. They do sell local prepaid SIMs at high cost; you are paying for
the convenience of having them before you leave the US.

However their international roaming products are a little different,
especially in that the pricing is more competitive. These are re-brands
of two well known products: "Explorer" (TravelSIM), and "Passport" (GT-SIM).
I have the Explorer and you can even check your balance from the TravelSIM
website ... proof of origin. As noted above, you can read about both of
them on the prepaidgsm forums.

For the US traveller, the Telestial advantage is being able to pre-arrange
auto-recharge via a credit card, charged from the US, without any bank
worries of having to explain charges from abroad when you are incommunicado
and out of the USA.