Have you been prompted for the software update yet? If not there is a software update which will address the issues you're experiencing. Click here for more information. Also, it's always a good idea when changing or updating any software to backup your information first, there are several applications on the market that will allow you to backup contacts, applications, text, etc.
I have a LoS problem with my Galaxy S2 Epic. The phone will either show a 0 with a strike through it or show bars for phone service but not service. I also have had the phone just cut out while I am on a call and then the phone freezes up and will not hang up the call. I hope this gets resolved because I pay way too much for this service not to be working and I use the phone for work. Time is Money Sprint get it fixed!!!!!!
This is actually a very common problem for the new samsung galaxy s2. Everyone I know has a problem with 3g, 4g, and cellular service constantly going in and out. Supposidly there is a patch that android is working on to fix this for our phone. This is pretty frustrating and I live in the new york city area.
Did you just recently start having issues or has this always been an issue? What does Sprint.com/coverage show for your location you're having the issues at? There could be a number of different causes for losing signal, if you post your zip code I can check to see if there's any current outages listed. Are you the only one having issues or do you know someone else with Sprint having same issues?