The ICAP is a method of representing an Ethereum address with a built-in checksum and in a way that is compliant with most bank software due to compliance with the International Bank Account Number (IBAN) format. But many block explorers and other tools are still using the raw hexadecimal representation for Ethereum addresses. Which Ethereum clients/wallets/apps actually support the ICAP?
Utilities for handling ICAP (Ethereum in IBAN) encoding
fromAddress(address, print, nonstd)- try encoding an address into an IBAN
fromAsset(asset, print)- try encoding an asset description into an IBAN
toAddress(iban)- try decoding an IBAN into an address description
toAsset(iban)- try decoding an IBAN into an asset description
encode(address/asset)- encode an address or an asset description into an IBAN
decode(iban)- decode an IBAN into an address or asset description
encodeBBAN(address/asset)- encode an address or an asset description into a BBAN
decodeBBAN(bban)- decode a BBAN into an address or asset description
Status of Ethereum Wallet 0.3.8 (Beta 5)
Not yet implemented source
Geth does not support ICAP yet. It's planned for the 1.4.1 release which are scheduled sometime after the Homestead release.
Eth does support ICAP, it's build in for a while now, but I never heard of anyone actually using it. I would recommend using it with care.