Ringtones for Phones

Hi! I need your help (:
Should I keep my current phone, shown here: http://www.wireless.att.com/cell-phone-service/cell-phone-details/?LOSGId=&device=Sony+Ericsson+-+W760a+-+Red&q_sku=sku3020348 ? The first phone I bought had NO SERVICE at all, and we had to return it. Now, my replacement phone says I have an Inactive SIM at random times, stops vibrating, says I have new messages when I don’t, won’t turn on, ect.

Should I get another replacement and hope it works fine, or see if I can switch to the Eternity: http://www.wireless.att.com/cell-phone-service/cell-phone-details/?LOSGId=&q_tab=reviews&device=Samsung+Eternity&q_sku=sku3130239 ? Thanks SO MUCH! :*