Hi Luis,
Do you want IPsec or AnyConnect?
For AnyConnect:
iPhone User Guide for Cisco AnyConnect Secure Mobility Client, Release 2.4.4
http://www.cisco.com/en/US/docs/security/vpn_client/anyconnect/anyconnect24/ios4.2-user/guide/iphone-ugac-ios4.2.html
Please check the license requirements for the iPhone with the AnyConnect client on the ASA (such as the
"AnyConnect for Mobile : Disabled" option).
For IPsec just configure the IPsec client on the iPhone and the ASA will have the same settings as if you were connecting from a regular machine.
Thanks.
Please rate if it helps you.