If you open the people app, hit menu, then view, it will list the number of contacts you have on your phone and what they are stored on (Phone/SIM/Google etc).
You shouldn't have to worry about limitations, you'd need quite a lot of them before you'd run out of space. You can also sync your contacts to your google account so you don't need to worry about them if you need to reset your handset. Is that an option?