Take out the mircrosim card from the Iphone 4 and put it in your different phone. You will need a microsim adapter as Iphone 4 does not have minisim card. The adaptor costs only 99 cents on ebay. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260629146001&ssPageName=STRK:MEWNX:IT#ht_2799wt_1139 
Also, you can fix your broken Iphone. Look for Iphone repair on Craigslist or your Yellowbook. 
This youtube video-http://www.youtube.com/watch?v=rzGBWKXZ7Mg might also be helpful.