The number 1234567891 keep populating on caller ID at work & on co-workers cell phones.?

That's someone calling from Skype or a similar VOIP setup. It's a great prank... You can actually put Skype on a PSP now and call co-workers from any wifi access point.

I have been getting the same call on my phone, It's not someone pranking you using Skype. I picked it up on accident and it was one of the many fraudulent 'auto warranty expiration' messages that have been going out to random people for the past year or so.

Best thing to do is just ignore it, this is the second time it has happened to me. The first time I googled the number and there were literally hundreds of other people who had been called by the same number with the same auto warranty message. I just ignored it and after about a week, the calls just stopped.