To see the Enterprise Activation icon, the BlackBerry must be running OS v4.0 or higher. The 7730 will not run OS v4.0, it doesn't have enough memory. I would suggest looking at one of the newer models with 64 MB of memory. If your wanting to stick with a GSM/GPRS device you might look at the 7290, 8700, and the 7100 series. You can compare the different models HERE
With that all being said, you can still use the 7730 if you want to, you just have to activate it differently. The model is past its prime, but still functional.