BT Remote iPhone

You can use this: http://www.iospirit.com/index.php?mode=view&obj_type=infogroup&obj_id=24&o_infogroup_objcode=infogroup-23&o1_infogroup_objcode=html-141&sid=8776784G0d456a28569b256a
But it is WiFi, not BT, so you might be better off just buying another remote.
MacPro Dual Core 2.66 Ghz, MacBook Pro 15", iPhone 3G Mac OS X (10.5.6) AEXs, Red 2G Nano, Red Shuffle, 160 GB Classic, White 60GB 5G

The remote that came with your iMac is not a Bluetooth remote, in fact its an infrared remote. The iPhone cannot be used to substitute for that, as it has no IR transmitter (nor could it be used as a Bluetooth remote, since the profiles dont support that).
You can purchase a replacement IR remote from Apple:
http://store.apple.com/us/product/MA128G/B
17" CD MBP, iPhone 3G, iPodTouch Mac OS X (10.5.6)  since the e