It's basically utility theft (although not as dangerous)
It's like bypassing an electric, water, or gas meter. Legal issues are the least of your worries when tampering with a gas or electric meter, as doing so is outright dangerous and many people have been killed in the process (including innocent people such as children and other tenants of the building involved) not to mention countless dollars of property damage.
The prosecutors should use their limited resources to go after people who steal gas and electricity as those people are putting people in danger by tampering with gas and electric lines. Gas can cause explosions and electricity can start fires not to mention the electrocution threat.
I think probation and restitution would fit the bill for modem hacking, save the jail space for the gas and electric thieves and they are a greater danger to society.
The greatest threat besides criminal charges for tampering with a water meter is flooding the basement.