The situation you describe is pretty common: how to give your user access to more data than they can possibly see in detail at once.
There are several ways to answer the question and the correct answer is completely subjective: it depends on what your user is trying to see or do with the contacts. Before you can really get a satisfactory solution, you need to know what the users are going to use the contacts for.
Just guessing (but you would know better than me!), I'd expect there are two things they're doing:
- Lookup: Looking for a specific contact and they already know their name/handle.
- Explore: Looking for a specific contact but they can't quite remember their name/handle. Or they're just browsing.
If you do filtering for all the solutions, then the Lookup goal is pretty much in the bag. The Explore goal is the one you want to design for:
- Random Subset: Its not a great way to browse since you're basically left with a subset to browse and then you must explicitly filter to see anything new. Hard to filter when you don't know exactly what you're looking for.
- Infinite Scrolling: seems like a popular solution these days. I find it cumbersome, especially if you are 'infinitely' scrolling thru 1000+ contacts. Probably not great for the Explore goal.
- Paging: Also cumbersome - but perhaps if the paging is tied to alphabetical sorting this could work well.
- Threshold limiting: so...simply relying on the filtering? This may be bad in some corner cases in which the user applies one filter and they don't see anything b/c the threshold still isn't met (maybe there are a lot of people with the last name Johnson, which is what you searched for). Plus, I think the ability to browse is important when you don't know what you are looking for.
I think if I were in your shoes, I'd introduce some clustering of the contacts. I doubt that the 1000+ contacts is much of a performance problem (in less you're talking a million!), so the 10000+ is really a user constraint: they just can't view 1000 contacts at once.
I'd suggest introducing some clustering, probably by the last name or last name and first name. Then present the user with a way to drill into one cluster but fold up all the other contacts so they're aren't immediately visible. Something in the ream of the accordian/rollodex paradigm. This gives your user the illusion that they are working with 'all the contacts'. Probably introduce a minimal number for each cluster so that if the cluster is sufficiently small you don't bother showing it (ie, why show a cluster for 2 or 3 or 5 contacts - just show the contacts). As filters are applied then, the clusters melt away.