I'm not sure, nor can you be without contacting the carriers that will have it since it could vary depending on where you live and what carriers are available.
Not to mention it's actually not been released yet.
My iPad1 has a sim card. I believe that the Verizon versions do not but you can't use Verizon iPads in many countries outside the USA anyway so there is no need. Verizon uses the old CDMA technology not used widely in this little world of ours whereas AT&T is GSM. Huge difference.
I should probably qualify my statement. I interpreted your question to be one of a security nature. The sim card can be locked so that others can't access your 3G network.
If your question is whether or not it locks other carriers out besides AT&T and Verizon, I assume it will be unlocked like the first gen iPad. In looking around there seems to be a bit of confusion, but the overall consensus seems to be that as long as you can get a compatible GSM sim card, the iPad should be able to be handled by other carriers--especially in traveling to other countries.
My apologies if I misunderstood the initial question.
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