Our residential service includes one phone line, but our small business (or SOHO) service comes with two. It's also 2x1Gbps broadband, twice the capacity on that too.
Pricing is also about double the cost of residential service, $90/mo for the first year, then it goes up to $100/mo.
Because we see very few folks asking to migrate between these two products, there isn't an automated way to do so. It's basically a new service order deployed by an installer, who brings a different ONT which provides 2xRJ11 (voice) and 4xRJ45 (Ethernet), replacing the "1+1" unit you have today.
If you'd like to consider that or have additional questions, contact sales via one of the methods listed on the website at https://www.sonic.com/support