This is normally a feature that needs to be supported by your device, whether this is a softphone or an ATA. It is difficult for us to keep track of various softphone vendors and their support of Call Blocking - it is best to contact them directly with this question. 

In general, if you asked us to enable e911 on your account, we will send the phone number associated with e911 with all outgoing calls; you can set the Name sent in the Caller ID info to anything you wish, straight from your softphone or ATA. If you subscribe to one of our plans, we can change the phone number we send as Caller ID on your outgoing calls to something else, such as your cell phone number. We can set up manually an arbitrary Caller ID to be sent out, other than the number you ordered from us (e.g., your cell phone number) so that anybody you may be calling from your VoIP number will call you back to your cell phone. We plan to offer this feature on our website on a self-serve basis in the future, but for now, insofar we need to set it up manually, we will charge a small fee (currently $2) for initialization. We cannot enable e911 for a number that is not ordered from us, so if you choose to use a different number than your actual number for Caller ID purposes, we will have to disable e911.

If you purchased an ATA from us, see in particular Step 12 in the PAP2T setup page. You can set the Call Blocking code to anything you like. The default is *81# for per-call and *67 for quasi-permanent blocking (where "#" is the actual phone number you are calling). To deactivate Call Blocking set by *67 you pick up the phone, dial *68 at the dial tone, then hang up; all subsequent outgoing calls will no longer have the outgoing Caller ID blocked. You can set the Call Blocking codes to something else or you can switch these codes among themselves if you wish, just make sure they do not interfere with service-specific codes, such as Voicemail.

Since we have no control over your devices or softphones, we cannot guarantee that Call Blocking will work; it is best to learn how to use it through trial and error.