I live in the States but I travel back to Canada frequently. I currently use a $30 per month, auto-updated Virgin mobile plan (which I really like) on an iPhone 5. Can I use the same plan on a new blackberry z30? Is there some limitations in terms of companies, or can an Unlocked bb use any service provider?
You would just need to make sure that you get the right model. If you're talking about Virgin Mobile US, there is no Z10 or Z30 that will work. If you're talking about Virgin Canada, get the Z10 STL100-3 or the Z30 STA100-5.
Here's the link to the page for bringing your own phone to Virgin Mobile Canada:
Get a SIM Card and bring your own phone and number to Virgin Mobile - Virgin Mobile Canada
Each BB10 model has multiple variants for different types of networks. As Raino just posted, for Virgin Mobile in Canada, you can use Z10 STL100-3 as well as Z30 STA100-5. (There are variants of Q10, Q5, Classic, and Passport that will work too.)
Basically, since Virgin Mobile Canada is owned by Bell Mobility, any device compatible with Bell (or Telus) will work on Virgin, providing it's unlocked or locked to Virgin already.
The Virgin Mobile USA website isn't quite as clear. I didn't find any info readily available on bringing your own device with you. You'd have to contact them and ask, or search online for more info. Virgin USA isn't the same bands as Canada. There may not by a wholly compatible model, and I'm not sure which model would be best.
Virgin Mobile USA is a Sprint MVNO. And since Sprint never picked up the Z10 or the Z30*, there isn't one of either that will work on VM US. Plus, both Sprint and Virgin are CDMA.