As Voice over Internet Protocol (VoIP) technology matured, service providers began to interconnect VoIP with the public switched telephone network and marketed the VoIP service as a cheap replacement phone service. However, E911 regulations and legal penalties have severely hampered the more widespread adoption of VoIP: VoIP is much more flexible than landline phone service, and there is no easy way to verify the physical location of a caller on a nomadic VoIP network at any given time (especially in the case of wireless networks), and so many providers offered services which specifically excluded 9-1-1 service to avoid the severe E-911 non-compliance penalties. VoIP services tried to improvise, such as routing 9-1-1 calls to the administrative phone number of the Public Safety Answering Point, adding on software to track phone locations, etc.