Most SMS aggregators do not verify mobile numbers before sending a ‘delivery request’ to carriers. When you send SMS text messages, carriers/SMS aggregators will charge you, whether the message was delivered or not. So, there is no incentive for them to pre-scrub the phone numbers. In the US, 500,000 mobile numbers are either suspended or deactivated daily. Carriers fail to deliver 5~18% of messages due to invalid, suspended, deactivated, inactive, or unreachable numbers.
You can save a ton of money scrubbing for unreachable numbers prior to launching SMS marketing campaigns. www.SubscriberVerify.com can scrub for these non-mobile numbers that will never reach your customer at a small cost.