As of version 5.0.0 Mapsi supports WMS (Web Map Service), WMTS (Web Map Tile Service), TMS (Tile Map Service) and Slippy Map tile server protocols.

How to add a tile server
1. Tap the half circle on the left side of the screen and then from the menu that opens, tap the upmost icon (the one that looks like a gear)
2. Select the type of the server you want to add and set the URL. For WMS, WMTS and TMS servers the URL should be the servers URL without any GET-parameters. For Slippy Map servers the URL should URL to a map tile, e.g. http://c.tile.openstreetmap.org/5/16/10.png
3. Click Add and wait
4. If add was successful, you'll see a message saying "Map Service client added successfully..."
5a. If TMS or Slippy Map server was added, map configurations were made automatically and you should be able to see the new map in the Base map listing
5b. If WMS or WMTS server was added, only the information about the map layers the server provides was fetched but not any map configurations (configurations that define what map layers and in what order we want to use) were made. At the moment map configurations needs to be done by manually editing map_settings.ini.

Syntax of the map_settings.ini (found in ~/.config/harbour-mapsi in Jolla and in ~/.mapsi in N9)
[foo]
name=themap
title=The Map
type=baseMap

# Slippy Map server layer(s)
layer\1\server=[the URL of the server that has the layer (exactly same that is in the server_settings.ini), e.g. http://otile1.mqcdn.com/tiles/1.0.0/osm/%z/%x/%y.jpg]
layer\1\zoomLevels=8, 9, 10, 11, 12, 13, 14, 15

# WMS server layer(s)
layer\2\server=http://example.com
layer\2\name=[see server_settings.ini]
layer\2\scales=[see server_settings.ini, e.g. 19.95611393718550, 9.97805696859275, 4.98902848429637, 2.49451424214819]
layer\2\epsg=[see server_settings.ini, e.g 3067]
layer\2\transparent=[true or false]
layer\2\format=[image/png or image/jpg]

# WMTS server layers(s)
layer\3\server=http://example.com
layer\3\identifier=[see server_settings.ini]
layer\3\tileMatrixSet=[see server_settings.ini]
layer\3\tileMatrix=[see server_settings.ini]

layer\size=3


I'll update more information to this post later.