Citrix has partnered with Nokia on ICA clients for their Symbian devices for years.  I recently did an interview with the Nokia team on use of the Citrix ICA client for Series 60 3rd Edition devices such as E61, E70 and E90 devices for their Nokia Forum Pro.  These ICA clients can be downloaded from http://www.citrix.com/English/SS/downloads/details.asp?dID=2755&downloadID=165587&pID=186.

Snippet from the interview below: 

Helping enterprise IT departments

 The Citrix XenApp Client for S60 3rd Edition devices offers some very clear benefits to IT departments as well, Marano adds. "From an IT perspective, the flexibility of mobile devices can be scary," he says. "How do you encourage people to use them, but also make sure that they are used properly and securely? With this solution, the same infrastructure being used today for external laptops and desktops can be used to deliver applications to the Series 60 3rd Edition devices. Minimizing the number of technologies used to deliver business-critical data to end users regardless of device type, by standardizing on a single platform, is a key factor to consider."

The interview gives a good overview of use Nokia S60 devices, but also provides a pretty good overview on the use of mobile devices as a whole with XenApp.

The full PDF interview can be found at: http://www.nokia.com/NOKIA_COM_1/Developers/Success_Stories/Enterprise_&_productivity/Dev_succ_Citrix_SC_v1.0.pdf