GSM OK, 3G not?

How weird - found I could phone Chris OK, and then remembered that when I posted from the airport the phone could only get a GSM signal, so I just switched the phone from dual mode to GSM only, and hey presto - it connects and sends OK. Not sure if the problem is with the networks here or with my phone and / or sim card. But at least I've got a means of connecting, even if a slower one than I'd like.