Issue:

Due to the recent changes in call filtering from mobile carriers we've encountered issues with the dialer where the calls are blocked by the mobile carrier (for example T-mobile) and are not connecting the agent to the dialer session or the lead to the agent when the dialer session is already active and marking the lead number as invalid.

We have contacted Twilio support in this regard and their response was as follows:

Our Carrier Partner sends us a 608 rejected SIP response code.

"608 rejected" status signals that the call was rejected by an intermediary VSP or its call blocking and labeling analytics company (for example T-mobile). So T-mobile is blocking any call traffic it sees incoming for the T-mobile Destination Numbers.

Additionally, if we change the Carrier preference, it would not matter since the calls will still have to pass through T-mobile analytics system.

And since T-mobile is not over immediate carrier, we have no control over how T-mobile chooses to filter call traffic.

Therefore, the best option for you here would be to submit a request to T-Mobile via their Call Reporting site - https://callreporting.t-mobile.com/ for the numbers that have been inappropriately blocked.

Ultimately, and unfortunately, terminating carriers are the entities that control call filtering and labeling of calls as spam or not and whether they are blocked. These carriers have analytics that looks for certain calling profiles, and often times their analytics cause false positives in terms of legitimate calls being filtered.

Solution:

So far the only solution to this issue seems to be to register the telephone numbers, your cellular and your virtual number in the CRM, with the analytic providers. To reach the major mobile carrier's analytic providers, please register the telephone numbers at www.freecallerregistry.com. Here, you can register your phone numbers for legitimate calls to the major US cellular providers. Please note, this process can take a few weeks to complete.

To reach T-Mobile's analytic provider directly to register numbers, please go to www.calltransparency.com to register numbers. Going direct to the analytic provider has a faster turnaround of being registered / call being delivered to end user.

Another option for T-mobile would be their Call Reporting site - https://callreporting.t-mobile.com/ which is used for the numbers that have been inappropriately blocked.

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Dialer calls are not connecting to the agent or the lead due to the mobile carrier rejection - SIP 608 error

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