Inteliremote + Intelliphone iPhone/Ipod app does this and supports the following hardware IR blasters....

o USB-UIRT http://www.usbuirt.com
o RedRat UIRT http://www.redrat.co.uk/
o BitWise BC4/BCX1 IR Blaster http://www.bitwisecontrols.com
o GlobalCache GC-100 or iTach IR Blaster http://www.globalcache.com
o Keene IRAnywhere KIRA IR Blaster [Link: keene.co.uk]

Check out Intelliremote...

[Link: melloware.com]

check out the Free iPhone companion Intelliphone...

[Link: melloware.com]