if I directly purchase this custom content...
As a general rule, "intellectual property" is very different from tangible property - arguably, "intellectual property" is a misnomer. Trying to apply concepts from property law (such as "a thing has a single owner, who can do anything not illegal with it as they please") is fraught with danger.
You would generally not "purchase content", but rather purchase a license for the content, allowing you to do various things. One of those things might be to "curate/edit this collection of recordings and present it publicly as an art project (probably just online)". Another might be to "to sell or otherwise profit from this". All that depends on what your contract says.
In an ideal world(?), contracts would all be detailed enough to leave no uncertainty about what is allowed and what is not. In the real world, a bunch of SMS can form a contract. For instance, the following is a contract:
A (version 1): Hey B, could you send me a clip of you waving at the camera? I will pay $10 for it.
B: sure
...but it’s not clear what A and B agreed as to what the clip would be used for. Saving and viewing on A’s device, probably yes; putting it in fullscreen in the next blockbuster movie, probably no. Showing it to A’s friends, putting it in an art project? That’s getting dicey.
You might have heard about "work for hire" granting full copyright control to whoever pays for the work to be created. In the united-states, the above exchange does not explicitly designate the content as work-for-hire, as would be required by 17 U.S.C. § 101 ("...if the parties expressly agree in a written instrument signed by them that the work shall be considered a work made for hire").
Here’s a better SMS contract:
A (version 2): Hey B, could you send me a clip of you waving at the camera? I will use it to make an art project, collating many such clips, and publishing that on the internet. I will pay $10 for it.
B: sure
Here there’s no question that B agreed with the proposed use. On the other hand, it’s likely than a different use would be deemed a copyright violation - the contract was proposed by A and should be understood as limiting A’s right to use the clip to exactly what they said they would do. If they wanted it to say something else, they could have sent a different SMS (see contra proferentem).