What happens when the maximum number of WCF connections is reached?

We have a service (A) that calls another WCF service (B).

Service B has default values.

<serviceThrottling 
      maxConcurrentCalls="16"
      maxConcurrentSessions="10" 
      maxConcurrentInstances="26" />

Service A can generate up to 150 threads, some of which can call service B.

What happens if service A calls service B with more than the maximum number of concurrent connections?

Does service B (WCF) call or store them in a queue?