You don't need to add a billing system for Internet use (like those used by large chains) because for a modest cost of $40/month (ADSL or cable-modem), you elevate your hotel to the level of "free high speed Internet access". Billing system adds large capital costs and adds recurring maintenance costs. The fact that you can attract one extra corporate guest per month because you have "high speed Internet Access" will easily pay for the cost of the ADSL line or cable modem line. Your reservation staff and web site and advertising brochures should clearly mention "Free high speed Internet Access included". "High speed Internet Access" is a necessity for business and corporate travelers.

There is a low cost in-room retro-fit wiring solution: use existing phone lines and add Passive Splitters from QLink Communications Inc. (College Station, Texas). Their etherSPLIT ™ allow you to add Ethernet signals on existing telephone wiring infrastructure. In order to do that, your existing phone lines from your "telephone room" to the guest room should have a pair of unused wire and less than 300 ft away, most telephone systems in small hotels will meet that criteria.
QLink's web site is http://www.ethersplit.com/ See this diagram on how the wiring looks like.

There is another way to send Internet traffic to rooms with existing cable TV wiring. The company who makes these boxes is called Corinex and these boxes can use either cable TV coax wiring or use the power line as transmission lines to carry Ethernet traffic to the rooms. Here is a photo of a Corinex cable TV to Ethernet converter in a hotel.

If retro-fit wiring cost is too high for all guest rooms to have Ethernet connections, install a simple D-link or Linksys router box in the lobby or lounge with a low-cost Linksys WRT54G and some "category-5" cables.

Corporate guests have basically 3 choices: no access (i.e., your competitors), free access (i.e., you), or expensive access using the large chains thinking (i.e., that in order to provide Internet access, the establishment must spend several hundred thousand dollars). Well, I almost forgot about the 4th choice, the dreaded "data port" (i.e., using a dial-up modem). "Free high speed Internet Access" is a market positioning strategy, the only downside is that barrier-to-entry is low, your competitors may found and read this article, got the idea, make a trip to the local computer store and install a similar system in a matter of hours !

The use of wireless Wireless 802.11 (aka WiFi) devices is extremely popular these days. By adding an WiFi Access Point to the existing network, you can make your hotel lobby "fully loaded" with wired access and wireless access. Most hotels are doing that today.

The following diagram shows how to add wireless Internet to the hotel's lobby for $60.

There are security implications in deploying 802.11 networks.

or use this scheme if you are starting a new installation to provide wireless access:

There are security implications in deploying 802.11 networks

Disclaimer

There are some technical issues which you should be aware of, these issues are common to all NAT-based firewalls of sharing Internet connection.

(1a) Your corporate guests with laptops should ask their IT department to enable the laptop to use DHCP before traveling. This is the exact settings as "factory shipped". As IT departments mature, this will become the standard setup for traveling employees.

(1b) Some special security (VPN) software installed on corporate laptops may prevent them from being used outside of their office, in that case, there is no cure.

(1c) Some non-Microsoft VPN software may be installed on their laptops that is not compatible with NAT firewall traversal (pass-thru), in that case, there is no cure.

(1d) As the IT departments mature, these non-firewall friendly security software will die and be replaced by  SSL-based VPN (called SSL VPN) who can traverse firewalls very well.

(1e) If the laptops have software firewall installed, they should be set to allow DHCP to work so that the laptop can acquire an IP address from the DHCP server on the LRP. Once again, as the world matures, this may become less of a problem.

(2) If these novice road warriors use Outlook Express as their email without doing a VPN, they probably cannot send e-mails (but they can still receive) because their ISP or corporate SMTP server will block mail relays from your IP address. In that case, you have to help them change their Outlook Express to use an "Outgoing SMTP" server that is friendly to your IP address. Typically this is your ISP's SMTP server. Sometimes your ISPs act unreasonable and they limit the number of emails you and your guests can send each day, you may consider adding an in-house SMTP server. All Linux boxes can be used as a SMTP server.

Recently, major hotels have routers that divert all SMTP traffic to their ISP's friendly email outbound server (geeks call them SMTP server). The only catch is that these servers do not generally like username and password, they prefer the simple SMTP port 25, plain text SMTP protocol. In other words, they don't accept TLS on port 25, they don't like username/password (geeks call authentication) settings on the email client.