NEW YORK ( TheStreet) -- Watch out, Amazon.com ( AMZN). The carriers may have found a way to eat some of your cloud lunch. Re-sellers. The market's assumption at the start of the year was that private clouds could not gain traction, because companies would rather buy cloud than try to build it themselves. So a bunch of startups are building private clouds for rent, and some are doing quite well at it. The largest of AT&T's ( T) new cloud re-sellers is Breakthrough Technology Group, based in Morganville, N.J., and known as BTG. It started seven years ago selling AT&T Wireless' mobile phone services. BTG is now the largest of what the company calls its Managed Service Providers (MSPs), which use its network and facilities to deliver private cloud. The MSP industry itself is sort of a muddle. Some firms calling themselves MSPs focus on machine-to-machine connections. Others do IT outsourcing. Others focus on mobile, which was BTG's original niche. A study from the IT Industry Association CompTIA last year called the MSP market "a work in progress". BTG itself can be a little hard to find, even online. BTG is also the common name for British Telecom Group , for a health services company also run out of London, for a banking technology consultant in Jacksonville, and for a Swedish paper company. On the New York Stock Exchange BTG is the symbol for a gold company. Founder Jeff Kaplan's original idea seven years ago was that corporations which wanted managed mobile resources would get them through his company, delivered through AT&T's network and with his management services layered on top of it. That business is still doing well. This week BTG acquired CelPro Associates of New York City, renaming it BTG Mobility, so companies whose employees are bringing their own phones and tablets to work can still be made part of a corporate network. But it's the cloud services that are taking off, Kaplan says. BTG has servers in AT&T data centers in a co-location agreement. BTG runs those servers as private clouds, using what Kaplan calls "best of breed" solutions like Juniper ( JNPR) for security, NetApp ( NTAP) clusters for redundancy, Microsoft ( MSFT) Exchange for e-mail, Citrix ( CTXS) for desktop management and VMware ( VMW) for virtualization and server management.