The Samsung Galaxy S 4G is the newer version of the popular Samsung Vibrant. For the most part, this Android smartphone is very identical in design and feature to the previous Samsung 3G Vibrant. Some call this the Samsung 4G Vibrant, but should be more appropriately called the Galaxy S 4G.
I own this phone and I can honestly say that it does not lag or perform sluggish whatsoever. It features the 1GHz Hummingbird processor which is capable of handling virtually all tasks, apps, and everyday functions of today's smartphones. It comes with stock Samsung-flavored Android 2.2, not Android 2.3 Gingerbread. Still, I have no complaints about the performance and functionality of the smartphone at all.
The screen is Samsung's signature Super AMOLED high resolution screen. Compared to 90% of mobile devices out there, this screen is extremely clear, responsive, and capable of playing HD quality pre-loaded Inception movie. The Samsung Galaxy S 4G is of course capable of high-speed cellular networks, but its availability is still limited. T-Mobile is the only one in my area capable of 4G, so I'm happy. But remember to always check the availability of 4G networks in the area.
The internal memory is a weak point for the smartphone. The smartphone struggles to maintain an arsenal of apps without the use of Apps2SD type of apps. Most popular apps supports SD transfer and installation now. But without a large internal storage, users are largely dependent upon the included 16GB MicroSD.
In essence, the Samsung Galaxy S 4G is a high performing Android smartphone. The screen is definitely nice to look at and its ability to perform lag-less functions is certainly welcomed over lots of sub-average smartphones out there.