According to an update on Nintendo's website Nintendo Switch owners will continue to enjoy online services for free until the paid service's official launch which is now scheduled for 2018. 

As previously announced, Nintendo Online provides access to online multiplayer gaming as well as a dedicated smartphone app that will connect to an online lobby and voice chat. Nothing has changed in regard to how the voice chat system is being described as it seems that Nintendo is sticking with the unconventional, perhaps cumbersome, system that is dependent on using a smart device to send friend invites, schedule play appointments, and to use game chat. This portion of the service remains scheduled for launch sometime this Summer. 

Nintendo's online paid service also includes access to downloadable games. For now, the games will include new versions of classic NES titles such as Super Mario Bros. 3, Balloon Fight, and Dr. Mario that will now include added online play. Whether the games will be permanent or only temporary downloads remains unclear. 

As for the price, the online service will be offered as follows:

• 1-Month Membership at $3.99 (USD).
• 3-Month Membership at $7.99 (USD).
• 12-Month Membership at $19.99 (USD).

Nintendo also notes that these prices are only for the Nintendo Switch and even after the online services go live, current services for the Wii U or the 3DS will not be affected.

Here's a chart breakdown of what services Nintendo Online will be offering:

Source: Nintendo