Check out the shell script written by the good folks over at Charles Proxy.
It installs automatically to the iPhone simulator. You should be able to use the same approach for Burp.
You can email yourself the cert to install it on a device. Another option is to modify your app to ignore the usual checks for the SSL cert, but don't forget to take it out for production.
Also the book Hacking and Securing iOS applications
has tons of awesome advice if you're into stuff like this.
Here's another answer that must be where I got the idea of using the Charles script: Adding a self-signed certificate to iphone Simulator?
And another answer that might be relevant: iPhone TrustStore CA certificates