Very informal. Spoke with one team member via phone for an "interview" and later followed-up asking for the internship before I accepted another offer, as this was the position I wanted to land. I was extended an offer and accepted.

I applied via third-party online application which screened potential interns. Afterwards, I was contacted via email and asked additional questions. This was followed by a brief phone call. After a few days passed, I followed up and was offered the position. The process was a bit informal, but it was only an internship afterall.