I just got a 755p from Sprint as well. I noticed that Sprint is completely missing from the TomTom setup as a data provider if you try to manually setup your device (which we'd have to since the 755p isn't listed). I also noticed that the Treo 650 selection won't work.
The first time I paired the two devices (GO700 and 755p) via Bluetooth, it listed that data services weren't available at all. When I renamed my phone to something a little more relevant (it defaults to the Hotsync name), I had to repair them and then it did show up stating that it offered data services. However, I failed miserably at getting Plus configured and working, so I'm going to put in a support ticket with TomTom. Although I can understand that they're not going to have a profile for every phone immediately available, this phone isn't all that new and Sprint is one of the more popular phone services in the USA, so I'm confused why the don't offer it as a service provider option in their configuration. To show how outdated that config is, they have separate listings for Cingular and AT&T, which are now the same company. Oh, well.
Truthfully speaking, I don't expect to get anywhere with this, but...it needs to be reported to them.