Exchange is extremely useful for syncing your data live to your phone, especially since Gmail added Exchange — but iPhones still only allow one Exchange account at a time. If you're jailbroken, here's how to add as many accounts as you want.
The folks over at the Modmyi.com forums figured this one out through some trial and error, and since the instructions require sifting a thread and picking out the important steps, we've narrowed down the process here. It looks a little daunting at first (and you should proceed at your own risk), but all it requires is a little bit of copying and pasting. In order to do this, you'll need to have jailbroken your iPhone or iPod touch and installed OpenSSH on it, as well as already have an Exchange account set up.
First, you'll have to SSH into your iPhone (which we've covered how to do before) and grab the com.apple.accountsettings.plist file from /private/var/mobile/Library/Preferences/. Download it to your computer and open it up with a plist editor (OS X has one built in, and there are a few for download on Windows). Be sure to back it up before you edit it, though, in case you mess up and need to go back to the original.
When you open it up, the Exchange account should be the first entry, and it should look something this:
<dict> <key>ASAccountEmailAddress</key> <string>[email protected]</string> <key>ASAccountHost</key> <string>m.google..com</string> <key>ASAccountMailNumberOfPastDaysToSync</key> <integer>0</integer> <key>ASAccountUseSSL</key> <true/> <key>ASAccountUsername</key> <string>[email protected]</string> <key>ASLastKnownProtocolVersion</key> <string>2.5</string> <key>Class>/key> <string>ASAccount</string> <key>DAAccountPersistentUUID</key> <string>47F76882-2678-41C7-91B9-5D1AD5F76BFA</string> <key>DAAccountVersion</key> <integer>2</integer> <key>DATrustSettingsExceptions</key> <dict> <key>b8fa0b7f 0e99494e e3210953 21fa4725 65454492</key> <data> YnBsaXN0MDChAdICAwQFW1NTTEhvc3RuYW1lWlNIQTFE aWdlc3QITxAUuPoLfw6ZSU7jIQlTIfpHJWVFRJIICg8b JicAAAAAAAABAQAAAAAAAAAGAAAAAAAAAAAAAAAAAAAA Pg== </data> </dict> <key>DisplayName</key> <string>Gmail</string> <key>Enabled Dataclasses</key> <array> <string>com.apple.Dataclass.Calendars</string> <string>com.apple.Dataclass.Contacts</string> <string>com.apple.Dataclass.Mail</string> <string>com.apple.Dataclass.ContactsSearch</string> </array> <key>Identifier</key> <string>F4EBDF4A-8C1E-486E-89A8-766C1C5D8170</string> <key>Short Type String</key> <string>Exchange</string> <key>Sync Identifier</key> <string>F4EBDF4A-8C1E-486E-89A8-766C1C5D8170</string> <key>Type</key> <string>Exchange</string> <key>Type String</key> <string>Exchange ActiveSync</string> <key>kASAccountVersionKey</key> <integer>7</integer> </dict>
Copy this whole section and paste it directly below itself — and then all you need to do is edit a few parts of the section you just pasted. Change the strings below ASAccountEmailAddress, ASAccountEmailUsername and DisplayName to correspond to your second Exchange account. You'll also have to change the last 4 digits of the DAAccountPersistentUUID to something else (it doesn't matter what it is, it just has to be different than the first account and have the same number of digits). You'll also have to change the last four characters of the Identifier string to something else — and make those same changes to the Sync Identifier string (so that the two strings match). Repeat this entire process (starting with the copying and pasting) for each new Exchange account you want to add.
When you're done, go back into your SSH client and upload your newly revised com.apple.accountsettings.plist file to the same folder you got it from, and you should be all set. You don't even need to restart your iPhone, if you just wait a minute it should ask you for the passwords and start syncing. Thanks, Jan!
Two Exchange Accounts (ActiveSync) [Modmyi.com Forums]