Telestial is a good company and they do provide a measure of support. They deliver on schedule and won't cheat you. Their prices are often higher than other providers and you should factor it in.
I'm presuming you are in the US based on the general feeling I got from your post. If so, another good place to buy unlocked phones is:
http://myworldphone.com/
Here is a link to another popular provider:
http://www.mobileplanet.com/
Compare the phone options there.
The explorer is an Estonian SIM. You can get good rates calling Estonia, but you can also get robbed blind. I would checkout what your rates are for calling that number. Alternatively consider getting a US phone number that can get internationally forwarded to his mobile. You can get free US phone numbers where you just pay the rate of the international forward from stanaphone.com, voicestick.com, and many others.
Competing SIMs are made by United Mobile with a Liechtenstein number and a whole series of providers from the Isle of Mann which give you a British mobile number. There is also a competitor form Iceland, but their SIMs don't have voicemail. Here is a link to a summary of the various plans:
http://www.prepaidgsm.net/en/international.html