Hi Michael,
Yes, you are right, the voice resources are split among virtual boards, 4 resources per board. The IPT and IPM are only limited by the license. You may have iptB1T4000, if you wish :-). You can also configure more than 1 IPT virtual board in gc_Start (I assume, we are talking about HMP). In this case you'll use iptB1, B2... but overall number of assigned resources is still limited by the license.