Apparently, some users have been experiencing an odd quirk with their Sprint version of the SGS2. For some, they lose 4G hotspot connectivity while using voice-calls. Luckily, Sprint is already aware of the issue and is going to be pushing out an update soon to fix it. This update also gives your wireless radio a much needed boost. It's a medium sized firmware patch so should take about 10 mins to complete, and should be coming at any time.