One of the benefits of Zen Cart being open source is that it gives you all the basic stuff you need for a store, well-tested and proven, while also allowing you easy access to add those bits that are specific to your business model.

Your business model, whilst not unique, is fairly specific and I think you'd have to do some custom programming to get all the bits you want in place.

If we were developing this for a client, we'd put the phones in one category, the gifts in another and the tariffs in a third. We'd then build a custom home page to make clear that they should choose one from each.

We'd set the appropriate config switch to not take them to the shopping cart when they make a choice, and add some code to instead move them to next decision.

We'd also use the Zen Cart extra cart actions functionality to ensure that they only make one choice from each category. There are examples of using this functionality in the wiki.

We'd probably suppress the quantity boxes too (which can be done through the configuration switches).