are you sitting comfortably? then lets begin ...
is it a series 5 or 5MX? I'm not sure of the differences between the two, but I used to use a 5MX so this may/may not work on the 5. it presumably has an infra-red port for talking to the mobile phone. if not, you'll need the Dacom card (well expensive). if it can talk through infra-red port, it can equally talk to a Psion Travel modem which, with the global adapters, can be plugged into a hotel phone socket. this should be cheaper than a "mobile" solution, but you'll need a roving internet service provider such as AOL. eg I subscribe with demon and can't connect to demon from overseas except by dialling back to the UK at £x per minute. AOL and others have local numbers (points of presence) all over the world. so many, in fact, that its hard to choose which to use.
the on-board help was excellent on the 5MX and enabled me to set up the psion in half an hour. once your psion is set up - and there are 3 or 4 things to set up on it, all you have to do with your phone or modem is set it to receive infra-red signals as the phone number you're about to dial and the account name, password etc will be on your psion. easy peasy.
I'm going on a similar trip, but gave my psion away as I can't be bothered to look after sensitive electronics and there's little mobile phone coverage when you need it. if I had the space/inclination, I'd take the travel modem if you can get one (£50-100) and the adapter for different phone sockets.