Pay phone cards?

I'm going to Japan next week, and will need to make a single phone call to a friend of mine when I'm at a subway station so she can pick me up.

What's the cheapest pay phone card that's available? (I'm assuming there are no more pay phones that accept coins?) Since it'll only be used for a single phone call, I'm not too keen on putting down too much money for it. And is it better for me to buy it at the airport or are they available for purchase at most subway stations? I'll be going to Tennoji subway station.

Many thanks!

NTT payphone will accept 10yen and 100yen coins as well. There are green phones and glay phones,but glay phones are more popular since they let you call overseas.
http://www.ntt-east.co.jp/ptd_e/mag_public/kind.html
Personaly,I think it's better just use coins instead of buying a calling card (500yen to buy) since you only use it once. (10yen a minuet for a local call)

Thanks a lot for your reply! I'll be calling a cell phone number of someone in Japan. I think that qualifies as a local call and I can use the green phone? (And the green phones are pretty common in subway stations and the such, right?) It makes me feel better to know that I can use coins for calling. This is literally the only call I'll be making in Japan, so that makes far more sense.

If you are calling a mobile phone, the phone charges will be more expensive than a "local call." "Local calls" are defined as calls made to a FIXED phone line number within the same city (for example, within Osaka city, numbers starting with 06, if you are calling from a pay phone located in Osaka city).

If you are calling from a pay phone to a mobile phone number, I think (someone correct me if I'm completely off) 10 yen gives you a 10 - 15 seconds. So I think it will be safe if you put in a whole bunch of 10-yen coins, or put in a 100-yen coin if you know from the start you are going to be able to reach your friend right off (since you get no change back from a 100-yen, if your friend does not answer and the answering machine kicks in or something and you have to hang up, that 100-yen coin is gone).