What happens if I have a .com domain, and don't pay for the next year in time?
- Is the domain locked for some time?
- Can anyone else register it the day after?
Your registrar may have a grace period (check with them!) but in theory it will be up for grabs.
Of course, if you have a trademark that matches the domain name you could probably get it back. But if you are big enough to have a trademark you should be paying a few years in advance and making sure to renew in a timely manner.
First of all, you should always pay your domain on time, preferably for a couple of years in advance (so that in case something "bad" happens between you and your registrar, or your registrar goes out of business, or you lose access to the account or what not and you need the time to sort it out), you don't lose your domain just because you only have a few days to resolve a major issue.
If you do not pay your domain on time, you can still get it back within a maximum of 45 days, but it's really about 30 days for most registrars (for getting it back, not talking about the ICANN process here).
This is the GoDaddy expiration process for a .com - I'm providing it as an example because of GoDaddy's sheer size.
Domain name: example.org Expiration date: 01/01/2011 (MM/DD/YYYY)
If example.org is not paid on 01/01/2011 at the latest, at some point during 01/02/2011 GoDaddy will change the DNS servers to a couple of its own (even if you're already using their DNS, they will still change), effectively disabling your entire domain and will put up a web page saying you have to pay for the domain, bla bla.
For the next 26 days you will be able to log in to your GoDaddy account, pay the standard registration fee and your service will be reactivated.
Should you fail to renew your domain after 26 days, you will no longer be able to renew it for the standard registration fee, and will also have to pay a reactivation fee to GoDaddy, which I know was last of $80. You will be ale to retrieve your domain until day 42. After that, it's not yours anymore.
Also, your domain will be up for auction on the GoDaddy Auctions site, from day 26 until day 36, should anybody want to buy it (or should you want to buy it back this way so as to avoid the $80 reactivation fee). Should no one want to buy it by day 36, that auction will be taken down and it will go back to auction on day 37, for a limited time period, as a "Closeout" (cheaper). Whomever buys a domain in such an auction is not necessarily awarded the domain. If you pay for it and the reactivation fee, you get your domain back and the auction winner gets his money back.