Mandevilla is on my shopping list every year. I usually opt for white. I try not to buy it too early in the season because it can only be left outside after nighttime temperatures consistently remain above 55F.
I always repot my mandevilla so that it can climb up the trellis that I already have. It requires some unwinding from the support that is provided in the nursery pot and sometimes that takes a while so a little patience is required. Often times, you can buy the mandevilla in a good-sized pot with its own small wooden trellis and there's nothing at all wrong with leaving it just like that. I saw a whole bunch at Home Depot a couple of weeks ago--healthy plants at a price that was well below that of the area nurseries.
I unwound this white mandevilla and planted it in my pot with my green wire trellis. The plant was sort of drooping forward and I thought it might need some immediate help locating its support. So I got some garden tape and loosely tied several of the plant stems to the trellis to give it a helping hand. Now there's no stopping it.
Bookshelf: Container Gardening Books