Regarding your plant, yes, it's a serviceberry. The dark blue berries are perfectly ripe, and you should harvest them immediately if you want to eat them. The pink ones aren't quite ripe yet. The berries on a single serviceberry bush tend to ripen almost all at once, rather than a few at time, so the birds don't always notice right away. Once they do, they will descend en mass and clean the bush completely, leaving you sad and berry-less. For several years now I have missed picking the serviceberries in the landscaping around my building, by waiting for it to get just a bit more ripe.
The question of "which plants can be confused with this plant" always comes down to which identifying characteristics you rely on most heavily. The way to safely identify an edible plant is to use multiple ID characteristics.
If you're just looking for plants with dark blue to black berries, then you could confuse it with the poisonous pokeweed (Phytolacca americana, also called pokeberry, as mentioned by bob1) and some nightshades. Also every vine that people sometimes confuse with grapes, such as moonseed (Menispermum canadense), Virginia creeper (Parthenocissus quinquifolia), vining nightshades, etc.
If you remember that serviceberry is a woody plant, then you won't be confused by pokeberry or nightshade. If you remember that it's not a vine, you won't be confused by any of the grape look-alikes.
If you're looking at landscaping plants, you should be aware that guides to "plants of North America" tend to focus on wild-growing plants. A completely different set of plants are used in landscaping, and the ones that don't grow in the the wild are usually ignored by such guidebooks.
In landscaping, you could confuse serviceberries with ...
- Aronia (chokeberry, notice it's not the same plant as chokecherry). Both are edible, and also easy to distinguish if you learn what each fruit looks like. The blossom ends of these fruits have very different shapes.
- Viburnum - there are lots of different kinds of viburnum used in landscaping. There are some wild viburnums with edible fruits. Viburnum trilobum (found in the wild but usually not in landscaping) has edible fruits Viburnum opulum (used in landscaping and sometimes escaped into the wild) has bitter, unpleasant-tasting fruits. Bitter usually means it's not good for you, but you would probably have to force yourself to eat many more fruits than your tastebuds want in order to make yourself sick.
- Silky dogwood (Cornus amomum), is a thicket-forming multi-stemmed shrub with blue berries. It's native to North America, and is common in native plant landscaping, but not otherwise widely used. I would have assumed the berries were not edible, but I've found several sources saying they are (for example).
- And more. The landscaping industry is constantly introducing new plants, so it's impossible to make a comprehensive list.
Here's a very similar look-alike that I haven't seen mentioned in any edible plant book or reference. Glossy buckthorn (Rhamnus frangula or Frangula alnus). Like serviceberry, buckthorn can grow either as a multi-stemmed shrub or as a small tree. It has light-gray bark of a similar shade. It grows in a wide range of habitats, from wet to try, full shade to sun. It's an invasive species, so it tends to insert itself uninvited into landscaping and natural areas. And it has black berries, of a similar size and shape to serviceberries. If you eat buckthorn berries, they have a cathartic effect (in the medical sense). In layperson's terms, they give you the runs, the trots, the "sprint-for-the-bathrooms". It could be a day-ruiner, but it's unlikely to kill you. (As North Carolina Plant Toolbox puts it, "This plant has low severity poison characteristics.")
Comparing Glossy buckthorn vs Serviceberry
Bark color and pattern
- Glossy buckthorn bark has pairs of horizontal white lines (the technical term is "lenticel"), about 1-3mm long, that look like equals signs
(image source: minnesotawildflowers.info)
- Serviceberry bark does not have noticeable lenticels. Some varieties have subtle, dark gray vertical lines, but these are not a reliable ID characteristic. The general appearance of the bark is a very smooth, matte gray.
(image source: USU tree browser)
Color of unripe and ripe berries
- Glossy buckthorn berries start green, then turn yellow, then develop a red blush on the yellow base color, until finally turning black (not blue). It's very common to see yellow, red and black berries in the same fruit cluster.
(image source: minnesotaseasons.com)
- Serviceberries also start green, but then develop straight to red, before becoming a dark blue (not black). As mentioned above, when ripe, almost all the berries on the same bush will be dark blue. A sparse few will be red.
(image source: backyardforager.com)
- In the above berry images, notice that the blossom ends are different. Serviceberries retain some spiky bits that look like remaining flower petals (actually they are the remains of sepals). Next time you eat a blueberry or apple, notice that they have similar spikes. Buckthorn berries lack these spikes; they have a smooth blossom end, with a tiny dot that you have to look very closely to see (it's too small to see in the photo).
- Peterson, Lee Allen, 1977. Edible Wild Plants: Eastern/Central North America, Peterson Field Guides Series.
- Thayer, Samuel, 2006. The Forager's Harvest: A Guide to Identifying, Harvesting, and Preparing Edible Wild Plants.
- Braun, E. Lucy, 1989. The Woody Plants of Ohio.
- Many years of personal experience in North America, identifying wild plants and plants used in landscaping, harvesting and eating edible plants (without dying), and controlling invasive plants (without being fired for killing plants I wasn't supposed to kill).