booking tickets for 2 from different cities

It's easy to book so you're routed on the same transatlantic flight (just book with connections at the same east coast gateway like Newark or JFK and ensure you're on the same ongoing flight) so I assume you want to be seated together on the transatlantic flight.

One way would be to book flights from your starting points to the gateway on one ticket and the ongoing flight as a separate reservation for the two of you. You may be able to check your bags through to Paris at the origin (best chance if the whole itinerary is on the same airline or partner airlines) but you may have to claim your bags at the gateway and recheck them.

Once you've decided on an airline, this may be a situation in which you should call the airline to book the flights. You'll have to pay a small fee to have an airline employee make the reservation, but this person will be able to link the two reservations together. That way, hopefully, you'll sit together, be reboo,ed together in case of delay, etc.

Separate tickets for flight to the gateway city and to Paris will likely increase the costs. I suggest you do a search on http://matrix.itasoftware.com/ and find flights that are the best price on the same airline and reasonably convenient for both of you. Then book the flights and choose seats next to each other on the flight to Paris and back to the gateway. This will work either the big 3 United, American/USAir, and Delta. Flights for more esoteric airlines (Icelandair, etc) might be trickier.
When are you flying? Looking at April, the big 3 prices are all the same (collusion?). $1348 from Columbus and $1468 from Portland. So pick an airline and a transfer point you can agree on and go from there.

I agree with both Sam and Bets. Choose to be on the same airline, then meet up for the overseas flight. One of you will be penalized a bit on the airfare and one of you will have a longer connection to wait for the other to show up - that's normal. I've done that many times, meeting up with friends for a trip.

Here is another alternative: open-jaw one of the tickets.

Have the friends meet up in the departure city ie Columbus. Get the Portland friend ("B") to buy just one 'one-way' ticket to Columbus, a day or two before you leave for Paris.

Friend A's ticket : Columbus - Paris - Columbus
Friend B's ticket : Columbus - Paris - Portland
- only friend B buys a one-way Portland to Columbus ticket

Once you factor in the cost of that one 'one-way' ticket, you can also price the total from New York as well and decide that meeting up in New York for a day or two before Paris might just pay for itself, too!! Orlando or Vegas might surprise you that way as well (routes popular with European tourists).

Friend A's ticket : New York - Paris - Columbus
Friend B's ticket : New York - Paris - Portland
- both friends buy a one-way ticket to New York

Once you have the tickets to Paris worked out, then I agree with Bets about phoning the airline, so that the two ticket files are linked.

We do this frequently with our son and dil. You need to use the same airline. With a little prechecking you should have a good idea of the flights you want. Call the reservation number for the airline, add in your friend as a conference call with the ticketing person. The three of you will then establish the booking. It works very smooth. And you are not the first person to do this.

One way would be to book flights from your starting points to the gateway on one ticket and the ongoing flight as a separate reservation for the two of you.

No.Horrible idea. If you are on a single ticket, the airline will protect you in the event of irregular operations (ie. flight delays for mechanical, weather, etc.) that cause you to miss a connecting flight and will rebook you to your final destination as soon as space in your cabin class is available.

If you're booking two tickets, you lose this protection. If your domestic flight (Ticket #1) is late and you miss your international flight, you are considered to be a no-show for the international flight (Ticket #2) . At this point, it is up to the airline (and really the individual customer service agent) if they are willing to 'marry' your flights after the fact and rebook you to your final destination at no additional cost or if they will still call it a no-show and require you to repurchase an expensive last minute walk-up fare to get you to your final destination.

Because I have weird airline karma, my rule is that if there have to be multiple plane tickets involved in a trip, there should be at least 8 hours, and preferably 24 hours, between arriving on ticket #1 and departing on ticket #2.

It can be booked online very easily. Each of you need to make your own reservations from your respective home airports. Select the same city on the east coast for you international departure such as Newark, NYC or Atlanta. Then select the same flight number to depart from that city to Paris on. Do the same to return, choose the same flight from Paris to the east coast and then go your separate ways. Once you have your reservations, you can then select seats next to each other on flights from the states to Paris and vice versa. Once your reservations are made you can also call the airline and have them link the two reservations together, so if anything changes for one, it will change for both reservations. You will need both of the confirmation numbers to do this.

Selkie, that is exactly why I made a point of saying that if a one-way ticket is bought separately to get to the departure point for Paris, that it be for a day or two BEFORE the intended date to leave for Paris.

Ang84355, that is exactly how we usually do it. We always agree to simply meet at the departure gate for the transatlantic flight segment.

However, this coming January, the friend that is starting the trip with me to Italy, felt more comfortable joining me here to start. She decided to open-jaw her ticket: leaving from my city to Rome, then returning to her city. She will be arriving in Ottawa the day before we are due to leave for Rome together. This is just like the first alternative that I explained above.