While multiple Grasshopper numbers can be added to the same account you only get one set of extensions per account. Meaning you cannot have duplicate extensions for each of your numbers. However, you can have different main greetings for each of your Grasshopper numbers that have different messages and direct callers to the appropriate extensions.
For example, if you have 2 numbers you can use your existing set of extensions and direct incoming calls for Number A to extensions 1 and 2 while Number B can use extensions 3 and 4. Both numbers cannot have different extension 1’s on the same account.
NOTE: Each additional phone number you add beyond what is included in your Grasshopper subscription will cost an additional $10 or $5 per month, depending on your plan.
To add a number to your Grasshopper account, see How do I add another number to my account.