Depends what you mean.
There's 'offline by default at home' and 'offline by default overall'. And it can blur.
At least as far as 'offline by default at home'
After (1) my dad retired and bought a brand new fancy PC with some of his unused leave time [0] we wound up getting a dial-up account [1] but sometime around 1998/1999 [2] we wound up just getting a secondary phone line; somehow the 'internet' was so magical to all of us kids or young adults, that it was better for our parent's budget to just pay for the extra phone line.
Still, it wasn't even 56K. Phone lines in my area of Detroit were garbage, if it did connect at 56K it was unstable as hell, 28.8 was the 'reliable' connection rate, to the point you prayed that was what it connected at.
For 'offline overall' the change can be more blurry, at least in my head. I blame work phones, my PSP's WiFi capabilities, and the HTC Dream (released 2008) as the slow shift for me.
FWIW, I did enjoy my time on WinPho, where the siloing of the OS and lack of apps, led to a quieter time where my phone was a 'phone' (and honestly, still a better one at calls, SMS, or driving navigation than than my current one) rather than be tempted by anything online.
It's weird to think about. Before I went to college, Online (thanks to that dial-up) was an escape from the prison of my home and where I lived. But now Online feels more like a tug away from enjoying life.
[0] - P2 266 MHZ 32MB Ram, 2(? might have been 4) GB HDD...
[1] - Thanks Diablo for the WorldNet trial and thanks WorldNet for having the practically unlimited usage thing [4]
[2] - My oldest Sister was Driving home from College and the engine on the car blew up while I was online. She couldn't call for help. [3]
[3] - How's that for a technology shift though, as far as taking things for granted (i.e. call waiting being seamless and not costing extra per month.)
[4] - Except for the bit where when AT&T somehow figured out we were using a 'Share-dial-up-over-LAN' a few years later, had to switch to Mindspring after dad had me do the research.