You can make multiple calls from the same Voxalot account at the same time.
You may need multiple SIP devices or soft phones however.
Are you calling other VoIP accounts or traditional Land line numbers?
If calling regular phone numbers, your service provider must also support multiple calls or you need multiple providers.
WebCall is a feature to set up a call between two endpoints from your Voxalot account.
This requires a Premium Voxalot service.
Please also refer to the Voxalot FAQ -
Main Page - Voxalot FAQ