Download the aim.alx here

Place the aim.alx in the following path C:\Program Files\Common Files\Research In Motion\Shared\Loader Files\8310-v4.5.0.69_P2.7.0.72 (I am running 4.5.0.69, yours will be different)

Open up Blackberry Manager and click on Application Loader

You will now see AIM in the list, check it and hit next to complete this step.

Now download the Service Books from here

Use Desktop Manager again and click on Backup and Restore

Click Advanced

Click File > Open > Choose Service_Books.ipd and send it over.

Once this is done AIM will now work on your phone. It least its done for me.