"trips over" here means to fall over, meet difficulty or fail. An analogy is tripping over an obstacle on the ground. You meet a difficulty and maybe hurt yourself because your foot stumbles/'trips over' this obstacle. You are 'tripped up' or hindered from proceeding.
Also, a 'line' can be a separation point or even a barrier - sometimes easy to pass through, sometimes more difficult.
The poor meet this imaginary line or barrier of the 'high speed' era (internet age), but they 'trip up'/'trip over it' . They can't get past this barrier/line as their poverty (literacy skills, perhaps) hinders them or creates difficulties for them to use the high-speed' internet.