From my understanding, a jailbreak won't be necessary. I thought I read somewhere that the new iPad isn't carrier locked (except that the AT&T and Verizon can't go back and forth). If it's unlocked, I'm hoping to use an AT&T model with a T-Mobile Monthly4g sim card. For $30, T-Mobile gives you unlimited data, although only the first 5 gigs are at 4g speed. I was checking online and it seems like T-Mobile uses an LTE band that is compatible with the new iPad.
http://prepaid-phones.t-mobile.com/monthly-4g-plans
Does anyone know if this thinking is right or wrong or will we not know until people get their iPads?