We are going to purchase Cisco 7606 router with SUP32 and Basic IOS.
My question is: Do we upgrade the IOS in Advance Enterprise Service/Advance IP Service in future if we required?
Does Cisco lock the IOS that we will purchase right now?
No, the IOS is not locked to the version you buy the Sup with. However, you are expected to pay the necessary fee for upgrading, even if you may be able to download the version you need from CCO.
Cisco has for many years been using the trust model for IOS, i.e. trusting their partners and customers to pay for the IOS type they use. So if you have bought a Base image and at a later time need Advanced, then you will be able to download and use the Advanced image - but you are violating the trust.
It's up to your own honesty in the end, but if you misuse the trust, then you might be penalized if or when Cisco finds out. And it is an illegality.