Index: zaptel-base.c
===================================================================
--- zaptel-base.c	(revision 854)
+++ zaptel-base.c	(working copy)
@@ -745,6 +745,20 @@
 	unsigned char *newbuf, *oldbuf;
 	unsigned long flags;
 	int x;
+
+        /* Allocate history buffer, or not.  This probably shouldn't
+	 *            be here, but it's convenient */
+       if(!j)
+       {
+          if(ss->history) kfree(ss->history);
+          ss->history = NULL;
+       }
+       else
+       {
+         if(!ss->history) ss->history=kmalloc(ZT_HISTORY_BUF_LEN, GFP_KERNEL);
+       }
+       ss->historypos=0;
+
 	/* Check numbufs */
 	if (numbufs < 2)
 		numbufs = 2;
@@ -3445,6 +3459,8 @@
 	unsigned long flags, flagso;
 	int i, j, k, rv;
 	int ret, c;
+	int k1, k2;
+	struct zt_history hist;
 	
 	if (!chan)
 		return -EINVAL;
@@ -3923,6 +3939,29 @@
 			}
 		}
 		break;
+	case ZT_GET_HISTORY:
+		if (copy_from_user(&hist,(struct zt_history *) data,sizeof(hist)))
+			return -EIO;
+
+		if (!(chan->flags & ZT_FLAG_AUDIO)) return (-EINVAL);
+		if (!chan->history) return -EINVAL;
+		j=hist.len;
+		k1=ZT_HISTORY_BUF_LEN-chan->historypos;
+		k2=chan->historypos;
+		if(j>0 && k1>0)
+		{
+			if (copy_to_user(hist.buf,chan->history+chan->historypos,min(j,k1)))
+				return -EIO;
+			j-=min(j,k1);
+		}
+		if(j>0 && k2>0)
+		{
+			if (copy_to_user(hist.buf+k1,chan->history,min(j,k2)))
+				return -EIO;
+			j-=min(j,k2);
+		}
+		/* Probably should assert j==0 here */
+		break;
 	default:
 		/* Check for common ioctl's and private ones */
 		rv = zt_common_ioctl(inode, file, cmd, data, unit);
@@ -5587,6 +5626,15 @@
 		memcpy(ms->putlin, putlin, ZT_CHUNKSIZE * sizeof(short));
 		memcpy(ms->putraw, rxb, ZT_CHUNKSIZE);
 	}
+
+	/* Store in the history buffer */
+	if(ms->history)
+	{
+		memcpy(ms->history+ms->historypos,rxb,ZT_CHUNKSIZE);
+		ms->historypos+=ZT_CHUNKSIZE;
+		if(ms->historypos >= ZT_HISTORY_BUF_LEN)
+			ms->historypos=0;
+	}
 	
 	/* Take the rxc, twiddle it for conferencing if appropriate and put it
 	   back */
Index: zaptel.h
===================================================================
--- zaptel.h	(revision 854)
+++ zaptel.h	(working copy)
@@ -143,6 +143,8 @@
 #define ZT_MAX_NUM_BUFS		 32
 #define ZT_MAX_BUF_SPACE         32768
 
+#define ZT_HISTORY_BUF_LEN       16384 /* Count of ulaw samples */
+
 #define ZT_DEFAULT_BLOCKSIZE 1024
 #define ZT_DEFAULT_MTR_MRU	 2048
 
@@ -289,6 +291,11 @@
 int reserved[4];	/* Reserved for future expansion -- always set to 0 */
 } ZT_DIAL_PARAMS;
 
+typedef struct zt_history
+{
+	unsigned char   *buf;           /* Sample buffer */
+	int len;                /* Length of buffer, in bytes */
+} ZT_HISTORY;
 
 typedef struct zt_dynamic_span {
 	char driver[20];	/* Which low-level driver to use */
@@ -604,6 +611,11 @@
 #define ZT_TIMERPONG _IOW (ZT_CODE, 53, int)
 
 /*
+ * Return history buffer
+ */
+#define ZT_GET_HISTORY _IOR(ZT_CODE, 66, struct zt_history)
+
+/*
  * Set/get signalling freeze
  */
 #define ZT_SIGFREEZE _IOW (ZT_CODE, 54, int)
@@ -1039,6 +1051,10 @@
 	
 	int		blocksize;	/* Block size */
 
+
+        u_char          *history;       /* History buffer, for pre-ring caller ID (ZT_HISTORY_BUF_LEN) */
+        u_short         historypos;     /* Current position within buffer */
+
 	int		eventinidx;  /* out index in event buf (circular) */
 	int		eventoutidx;  /* in index in event buf (circular) */
 	unsigned int	eventbuf[ZT_MAX_EVENTSIZE];  /* event circ. buffer */