You can't port forward port 5060 with a Fritz!box.
I also pose a question for you - why you want to port forward port 5060? The fact you're wanting to do this suggests to me you don't understand the major security issues associated with doing this. Port forwarding isn't necessary for 99% of VoIP setups, and should only be used if you fully understand the risks.
*Need help configuring your Linksys ATA or IP Phones for New Zealand? Check my blog post