The number of simultaneous calls or channels depends on the 2talk plan you choose.
You can confirm the default number of Simultaneous Calls or Trunks on the Voice Pricing Page. The number of trunks provided with your account = the number of simultaneous calls you can make. Trunks also = channels.
Purchasing additional cloud lines will add trunks/channels to your account. Each cloud line outside your plan allowance adds one trunk to your service.
If you require more simultaneous calls on your account, including high volume services please contact 2talk support. We will work with you to understand your requirements and provide pricing.