I don't think IVM limits the number of simultaneous calls (beyond the number you set in the line settings) regardless of the license, but I could be wrong.
I think the license only restricts the number of lines (i.e. SIP accounts or physical lines) you can use with IVM.
Things to note:
1) Each additional concurrent call is going to require more and more CPU power to handle and could cause the system to crash if it gets overloaded
2) Your VoIP provider may choose to limit the number of concurrent calls you can receive
3) Your Internet connection must be able to support very heavy bandwidth use (up to 180kbps per call)
A standard call using the default G.711 codec uses 87.2 kbps of total Ethernet bandwidth and this is just for one side of the call. So multiply that by two and each call is using about 174.4 kbps of bandwidth. Now let's multiply that by 150 calls... that would require 26,160 kbps of ethernet bandwidth. In other words your Internet connection bandwidth would have to be almost 26 mbps to support that load!
What I'm trying to point out is that even if IVM could support that many calls without crashing, there are many other factors which would likely prevent you from being able to handle that many calls at a time. It is of course a very different story if you use a low-bandwidth codec like GSM which would permit dozens of more calls using the same amount of bandwidth.