Although this is a common complaint in general about this phone, the fact that you had good signal at one time and now you are experiencing poor signal could be the result of many things. If you are on the Verizon network could due to increased usage of their services in your area and their lack of infrastructure to handle the increase load. This is also common, for Verizon. Some things you should to determine the fault, be it the phone or the service, is to go to a densely populated area, preferably in the city around major businesses and check the reception levels at various points. If you receive good reception in the city, but as you move further away, the signal reception becomes spotty, you need to contact your provider and provide details of your issue. They will not act until they receive enough complaints in that to fix the issues. If your reception does not improve within the city, the phone is the problem and the first thing to look at is to remove the battery for about 20 minutes and let the phone cool down and discharge all power in the unit. This clears any interference he phone may be causing. Short of that, if you did not drop it or you are not prone to putting it in your pocket and accidentally sitting in it or banging it against low lying counters and the such, you may need to take it in for service, The antenna is basically a thin flat ribbon that runs on the inside of the phone around the joint (the portion you flip with) to the top of the phone (when opened). This results in the ribbon wearing out and causing breaks or in fact slicing the cable rendering the antenna virtually useless. Hence no signal. I hope this helps and if there is anything I can do further to assist you, please do not hesitate to ask.
Here is a map you can view in order to see you areas signal reception and the score they received for signal quality.
http://reviews.cnet.com/cell-phones/samsung-renown-verizon-wireless/4599-6454_7-33394071.html?tag=mncolBtm;rnav
