You need to install something on his phone.
If you could do it with just a PC application then anyone could track any phone, a huge invasion of privacy.The easiest thing to do is to install google latitude on his phone (it's free from the market) and set it to update frequently and share his location with you.
His location will show up on your phone if you look on google maps, you may need to also install latitude and switch the latitude layer on in maps.He could always disable this but since you're paying the phone bill make it a condition of keeping the phone that he doesn't.
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