Understandable.

However, the AIM approach is much more secure, and an SSL certificate can be acquired for under $50/yr, and a static IP can be had for approx $2/mo extra on hosting plans.

Haven't looked at the SIM code in quite awhile to know what's involved in getting it up to speed. But I do know that there are lesser fraud risks when keeping customers on your site instead of sending them somewhere else to complete payment.