Tenshi no Uta Soundtrack (http://www.amusement-center.com/project/emusic/cgi/eggmusic_catalog-detail.cgi?product_id=1823)

I really want this, but I don't know how I can go about purchasing it. Can anyone help?

The linked website has Chinese and English translation available, implying that you could potentially purchase from overseas (they also take credit cards). I'll try it and see if it's possible.

EDIT: You actually need either a Japanese telephone number OR Japanese address if you want to log in with a Yahoo Japan account... You could use a fake address/phone number but I don't know how payment will go... Sorry, this isn't much of a help. :(

Is it really possible to buy from the United States? I'm purchasing some Asuka 120% and Sol-Feace albums.

Yes, it is possible. You should be fine as long you have a PayPal account.

Before you can purchase anything, you must register at Amusement-center (https://www.amusement-center.com/en/user/free.cgi)

When you're done with registration, login via AC and click on EGG MUSIC () to start browsing/purchasing (in Japanese only). And yeah, you can change the language on AC too, which is just as well, seeing that the payments will be made through AC's checkout ().

EGG MUSIC icons ()

1. Price (obviously)
2. Checkout (will refer you to AC's checkout)
3. Download (will appear after the payment is made/confirmed)

As for telephone/address... I used my own. No issues arose from doing so. Pretty sure payments will be made in Yen too, but don't worry about it as PayPal will do the conversion.

Yes, I've used this service before. They have some great old stuff. My Japanese is alright so I guess that helps but as long as you are persistent and you use Paypal you should be successful.