Nokia 6700 phone can be used in Japan?

Any idea whether Nokia 6700 phone can be used in Japan? How about iphone 4S?

If Nokia 6700 cannot be used, where can I rent a phone and SIM card? What are the charges?

Any idea whether Nokia 6700 phone can be used in Japan?

Yes, it should work fine for international roaming, but it will need to be unlocked if you plan to use it with a Japanese SIM.

How about iphone 4S?

Again, this should work fine for international roaming, but if you plan to use it with a Japanese SIM it will have to be a version that utilizes microsim, and it will need to be unlocked.

If Nokia 6700 cannot be used, where can I rent a phone and SIM card? What are the charges?

At a rental counter at the airport or from an internet based company via the mail. Phones cost from 200-500 yen/day, domestic calls are around 100 yen/minute (incoming free). Email charges tend to be rather insignificant, but sms charges are high (about 100 yen/each). Internet, when available, is expensive without special smartphone rental plans which usually cost around 1500 yen/day.

See this page for more info:

http://www.japan-guide.com/e/e2223.html

Thanks. But how to unlock the phone in order to use it with a Japanese SIM card?

You should call up your provider and ask whether they lock phones. Or just get a sim card from a different provider, stick it in, and see if the phone prompts you for an unlock code.