A: One number can only be connected to 1 sim card. Number of SIM cards per device depends on your device. We don't have a cap on the total SIM card number. You can get banned, but we try to limit it by not sending messages as fast as possible (our current limit is 3 seconds between messages). If you use custom speed (e.g. you send yourself via API), you can further decrease speed.
Carrier limit depends on your carrier. One of our clients easily sends 20k SMS / month to Canada via Bell, but in India I heard there is 100 SMS/day limit per SIM.
I think the content also goes into the equation, not just sending speed.