Please expand on what you are saying that you can't have data and phone at the same time?
I
read that you cant surf while your on the phone. I use a headset most of the time and I often will be looking for something for some reason while I am talking to them. I would be bummed if I can't do that.
It is possible to use Voice and Data services at the same time on certain networks.
If you're on Sprint, you can't at this time. If you're on Verizon, you can, as long as you have an LTE connection. The S5, like most phones, can't do SV-DO, (Simultaneous Voice and 3G) but it can do SVLTE (Simultaneous Voice and LTE).
On Sprint, it simply isn't possible at this time. Spark devices only have single radio functionality, which allows for efficient Multi-Band use. Once VoLTE is implemented, however, you should be able to use simultaneous Voice and Data, as long as you have an LTE connection and as long as Sprint decides to update the S5 for VoLTE. Until then, you can use WiFi if you need Voice and Data at the same time.
If you have AT&T or T-Mobile, you can use Voice and Data service simultaneously. This is because they use GSM, which supports simultaneous Voice and Data.