The number of calls that can be simultaneously received by a virtual number is determined by the number of channels for incoming calls, which is determined by the provider of the number. By default, mobile numbers have 1 channel, landline numbers have 2 channels, and 800 numbers have up to 100 channels. When a number has more than 1 channel, it is called a multichannel number.
To check whether it's possible to add channels to already connected numbers, contact your manager or the support team.