Earlier than planned, O2 and E-Plus are merging the UMTS network - Telefónica had announced this after buying its competitor E-Plus. The solution is national roaming in the 3G network.
The advantage for customers: network coverage is Telefónica- and E-Plus customers especially with regard to data applications. In urban areas Telefónica by roaming over the densest data network - according to their own statements. In rural areas, coverage by roaming is also to be improved.
For the customers, the changeover is simple: all customers will be changed over bit by bit. In order to use both networks, the mobile phone must be switched off and on once, after which it should be possible to use the other network (i.e. O2 for E-Plus customers and vice versa). The switchover itself then runs without further intervention for the customer. Actually, the merger of the UMTS networks was not planned until 15.04.2015 - Telefónica is thus well ahead of its own schedule with the launch of national UMTS roaming.
Despite the improved UMTS coverage now available from O2 and E-Plus, the expansion of LTE is set to continue: currently, around 62 percent of the population is connected to the Telefónica LTE network This figure is to be increased to 90 percent by the end of 2016. An important component of the network expansion: the connection of the base stations. Time will show whether Telefónica is capable of expanding the network backbone in line with the increase in the number of users.
It is also interesting to know whether Telefónica plans to merge the GSM (2G) network and the LTE network in the future. Although this would probably cause problems with frequency allocation, it would also result in an even better overall network for end customers. It also remains to be seen how Telekom and Vodafone will react to the "new" network.
Update from 25.04.2015: No roaming in Munich yet
Apparently, the changeover is taking place relatively slowly: a good three weeks after the announcement of the merger, here in Munich it is Fonic card it is still not possible to log into the E-Plus network (tested in Munich East) Telefónica will probably first convert areas where it makes sense to do so, rather than full reception with all four networks as here.
Update from 10.05.2015: In the meantime also roaming in Munich
In the meantime, o2 has also activated roaming in Munich: the ePlus network will be operated on a Motorola Moto G with Android 5.0.2with Fonic-SIM as "Fonic+", o2 itself as "o2-en“. Booking works without any problems, but after some time it seems to switch back to the o2 network if it is available - but there is no disadvantage as long as both networks have good reception. I haven't made any speed tests yet.
When the next steps will follow and o2 will also merge the LTE and GSM networks is still open - so far roaming only works in the 3G network.