Motumotu

Which is the best way to go to Interlaken Ost from Rome? Trenitalia website is showing the time and route of trains from Rome to Interlaken but the tickets prices are not available. Will I save money if make the booking of train tickets in advance, say two or three months earlier? If we purchase the swiss pass, which is the station nearest to Italy uptil which the it is valid.

Palenque

Interlaken-Ost to Spiez, transfer to mainline trains via the Simplon Tunnel to Italy - Brig is the last Swiss station so you will need a ticket from Brig to Rome - check out trenitalia.com for fares in euros but booking on the site, which has attractive discounts if booked far enough in advance, are hard to do for American credit cards - so you may have to buy in Interlaken or Brig, at full price but full fare in Italy is much cheaper than in other countries.
For lots of info on Swiss and Italian trains i always spotlight these info-laden sites: www.budgeteuropetravel.com; www.seat61.com; www.ricksteves.com - and for Switzerland www.swisstravelsystem.com.
Fewer and fewer trains go thru the border anymore due to a contretemps between Italian railways and Swiss - well mainly the Italians it seems so expect to change at Brig - but i think there are still some direct Spiez to Milan trains so try to located one of those so you do not have to change at Brig as well. Your Swiss pass will cover you on the train until Brig then your Italian ticket picks up so you do not have to get off the train. For current info on the update of the Switzerland to Italy trains and to see about booking a direct one i would advise calling www.budgeteuropetravel.com as IME their staff are absolute experts that know everything. Just not sure at this time of the status of buying an Italian train ticket in Switzerland - i assume it's possible but not totally due to the current snafu. You may have to get off at the first Italian station - Domodossola and do it - just don't know. For smooth travel book the Italian portion ahead of time thru a U.S. agent - i guess try trenitalia.com first but many say American credit cards often do not work and the site has always been terribly frustrating in many ways.

Ciao ciao

Palenque

For schedules of Interlaken-Ost to Rome i'd go to the German Rail web portal - www.bahn.de and if your date is too far in advance to be yet loaded then just put in any day that is as these trains will change little - but put in a Sat or Sun if that is in your plans as these timings may vary from weekeday trains. The bahn.de site to me is the easiest to use - it will not give you fares like www.sbb.ch will (like the fare from Brig to Rome perhaps - for Trenitalia to give you fares put in Domodossola to Rome - Dom'sola being the first Italian station after coming out of the Simplon Rail Tunnel - and again you can try booking an advance online discount if you cana get it to work. Bahn.de site is Wunderbar - even gives specific platforms for changing trains in Switzerland i believe (as sbb.ch does) - a good way to get to its English scehedule page go to the home page of www.budgeteuropetrave.com as they have on that a link to the bahn.de's English schedule page and they also give you several tips to fully use the great bahn.de site - finding such info as the routings of the trains, all the stops they will stop at (nice to have along to see if train is on time or whether your stop is approaching, etc.) and such info if seat reservations are obligatory before boarding, etc.

Motumotu

I was going through the website www.budgeteuropetravel.com to look for 4 consecutive days swiss pass. As per my understanding, I found that Resident of Italy cannot purchase the Swiss Pass through this website.

Also please advice me regarding the price and timings of the train tickets from Rome Termini to Interlaken Ost and Back. Trenitalia website is not showing the prices.

Palenque

a resident of Italy can purchase a pass from an American website but i think the regulations imposed on agents by RailEurope - part owned by Swiss Railways - prevent the mailing of such a pass to Europe - for whatever reason or perhaps the agency is aloof to send a pass, worth cash, to Europe since it would be hard to trace if lost - if you live in the U.S. they could i am sure or think so sell you one as Italian residents can indeed use these passes - or have it mailed to someone in the U.S. who in turn would mail it to you. But better for you, if in Italy, is to go to a travel agent in Italy and buy it there or just show up in Switzerland and buy it upon arrival at any train station - this would require however you getting off the train from Italy at the first Swiss station and buying the pass - slowing you down - if you have the pass already you will validate it on the train and thus stay on the train.