Thoughts on basic interaction

Lately we've been talking a lot of prototypes and planning around our application, but I was assigned user experience testing in my group so I've had the looming thought in my head, "how do we make this usable?" I've been looking at our application evolve in this aspect.

We started with the typical three prototypes, and we all agreed on the idea of a sliding drawer containing any sort of data. The initial idea had a list of contacts and a sliding drawer containing a list of tags/groups. We all agreed that this looked good and was seemingly intuitive. A teammate and I further agreed that it'd be a good use of screen space. This idea ended up tanking, pretty hard. We ran into several issues:

1. The code was restrictive. I spent several weeks trying to even get it to render on the phone, with minimal success. I still maintain that it's possible but it got to the point where we were taking too much time deliberating over the initial UI feasibility.
2. Users didn't like it. Although, because of the aforementioned problem we never got any sort of formal feedback, instead relying on drawings to show users.

Had users liked the view, we could potentially invest more time into making the view render properly, but because there was little to no positive feedback regarding the potential layout, it was scrapped entirely.

This left us with two more ideas. Both incorporated a list view to show contacts, simply out of efficiency and user familiarity. However, selecting the tags is where the two prototypes differed. Our prototypes are as followed:

1. The tags are selected using a single button which brought a dialog of check boxes.
2. The tags are selected using a spinner (combo box/drop down).

Prototype 1 actually ended up getting the best feedback from the users. Buttons are intuitive and if there's only one button it seems to scream, "Click Me" or "Submit/Finish" regardless of what the button actually says. I'm tempted to write several applications and have only one button and no text to see what users do. My hypothesis is that users will click it just to see what it does. I feel like users expect guidance and will otherwise fall back on "monkeying" with the interface to figure it out. If the button says, "Tags: Family, Doctors, Coworkers" will users know right off the hand that pressing it lets you choose more groups, or will it, in our application's context, send the text? If you pay for texting this would be a rough trial since your worst case costs you money (multiplied by how many contacts you send to!).

The spinner idea is very similar. In fact one could argue it's more intuitive than the button. Spinner's come with a small graphic arrow on the right that is essentially saying, "click me, there's more to choose from!" Having a spinner and a button seems more intuitive to me, but user testing might prove otherwise.