I have used the OptiMobile UniPhone for a months now and with the latest release 1.2.2 is the best mobile VoIP product in the market today. It was little problem in the beginning but the first version of P1 version was more the reason (bad WiFi drivers etc).
I test a lot of different Dual Mode phones (both GSM/3G and WiFi with VoIP SIP client) include Nokia E65, E61i, E90 and now also SonyEricsson P1 with OptiMobile UniPhone client.
If you compare SonyEricsson P1 with Nokias phones:
+ Uniphone has much better sound quality
+ Even with bad networks with lot of latency and jitter it is good quality
+ When I talk with OptiMobile they told me that next release also will support seamless handover between WiFi and Cellular networks. This could not any Nokia phone handle today
+ The WiFi and SIP setting is much more simplier to do in the UniPhone client
+ VoIP is also working pretty good over the UMTS networks. With flatrate data subscription it is possible to save a lot of money.
+ Great to have several SIP account and connect to different WiFi AP. I have set up one account for Home and one for Enterprise. In my home I call out thry my VoIP operator and in the Enterprise I call all my call thru our SIP based PBX system.
+ Compare with Fring OptiMobile Uniphone is working. According to OptiMobile website http://www.optimobile.se they has developed this VoIP client together with SonyEricsson. The most others vendors has try to design a own client without any cooperation. This is very difficult to success with this advance software.
+ In the Swedish Magazine Mobil http://www.mobil.se/programtips_visa.asp?pId=500 the OptiMobile UniPhone get 8 of 10 points in the last test recomend buy. And finally a great software as UniPhone is for 25€ very inexpensive. In my last trip to Australia I saved 2€/minutes for all my call home to Sweden with this software compare with a call over the cellular operators network. The payback time was 13 minutes!
It is possible to download OptiMobile UniPhone in SonyEricssons own application shop:
Also in Symbian gears shop in UK, USA and in a lot of other countries. Uniphone has been the most sold software during the last week: http://www.symbiangear.com/platform_...5,29252,267831
Also mobile 2day is offer the uniphone I Germany at: http://www.mobile2day.de/platform_ps...821&noreload=1