When a service qualification returns a warning "Above ground cabling detected" this means that some of the cabling (typically copper phone cable) for this connection is above ground. Usually this means the cabling runs between power poles.
This does not mean the service will not work, however it does mean that the performance and reliability of the connection may be more susceptible to weather such as strong winds, rain or natural disasters, or outside factors such as car crashes and other power-pole related incidents.
Please note that this is not a provider-specific error - this test relates to the copper cabling in the street running from the local exchange to the premises. This warning affects all connections of this type from all ISP's.
This qualification result is a warning only, you may still proceed with the connection if you accept the risks involved.