TomSoft

1) Jailbreak your phone. You probably already know how to do it.

2) Install a patched “MobileInstallation” file. But when moving to V2.1, I had some problems: the phone does not wanted to reboot and was vibrating every 2 to 3 seconds. To correct, this I had to do the following steps: (even if
the phone is vibrating and the boot was not finished, you still can connect to it using ssh)

 * chmod 775 to the MobileInstallation file (as before)

 But also:

cd /private/var/mobile
chmod 777 Applications
cd /private/var/mobile/Applications/
mkdir Documents
cdmod 777 Documents

3) Create a self signed certificate, named “iPhone Pwned Developer” (see apple documentation to create a self signed certificate)

4) In your project settings, add the following:

for Code Signed Identity, put “iPhone Pwned Developer” (the name of the certificate you just created)

In the general configuration set the values of PROVISONING_PROFILE_ALLOWED and PROVISIONING_PROFILE_REQUIRED to NO
(you can also do this by doing “sudo vi /Developer/Platforms/iPhoneOS.platform/Info.plist” and modifiy these two values)

In the Info.plist of your project, add the following:

for the key: SignerIdentity  add the value: Apple iPhone OS Application Signing

and you’ve done…You can install your self signed application from XCode

Note that for further project, you just need no to add the SignerIdentity key in the Info.plist and the Code Signed Identity in your poriject settings. The iphonesdkdev blog seems to also provides template for this now….

Sources:
http://www.demonoid.com/files/details/1621027 for correct V2.1 installation of MobileInstallation (but I did not had to do all the indicated steps)
http://iphonesdkdev.blogspot.com/2008/09/xcode-template-for-pwned-iphone-device.html
  for SDK installation